Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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CWE-665: Improper Initialization

Weakness ID: 665
Abstraction: Class
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used.

Extended Description

This can have security implications when the associated resource is expected to have certain properties or values, such as a variable that determines whether a user has been authenticated or not.

+ Time of Introduction
  • Implementation
  • Operation
+ Applicable Platforms



+ Modes of Introduction

This weakness can occur in code paths that are not well-tested, such as rare error conditions. This is because the use of uninitialized data would be noticed as a bug during frequently-used functionality.

+ Common Consequences

Technical Impact: Read memory; Read application data

When reusing a resource such as memory or a program variable, the original contents of that resource may not be cleared before it is sent to an untrusted party.

Access Control

Technical Impact: Bypass protection mechanism

If security-critical decisions rely on a variable having a "0" or equivalent value, and the programming language performs this initialization on behalf of the programmer, then a bypass of security may occur.


Technical Impact: DoS: crash / exit / restart

The uninitialized data may contain values that cause program flow to change in ways that the programmer did not intend. For example, if an uninitialized variable is used as an array index in C, then its previous contents may produce an index that is outside the range of the array, possibly causing a crash or an exit in other environments.

+ Likelihood of Exploit


+ Detection Methods

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.

Initialization problems 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. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Effectiveness: Moderate

Manual Dynamic Analysis

Identify error conditions that are not likely to occur during normal usage and trigger them. For example, run the program under low memory conditions, run with insufficient privileges or permissions, interrupt a transaction before it is completed, or disable connectivity to basic network services such as DNS. Monitor the software for any unexpected behavior. If you trigger an unhandled exception or similar error that was discovered and handled by the application's environment, it may still indicate unexpected conditions that were not handled by the application itself.

+ Demonstrative Examples

Example 1

Here, a boolean initiailized field is consulted to ensure that initialization tasks are only completed once. However, the field is mistakenly set to true during static initialization, so the initialization code is never reached.

(Bad Code)
Example Language: Java 
private boolean initialized = true;
public void someMethod() {
if (!initialized) {
// perform initialization tasks

initialized = true;

Example 2

The following code intends to limit certain operations to the administrator only.

(Bad Code)
Example Language: Perl 
$username = GetCurrentUser();
$state = GetStateData($username);
if (defined($state)) {
$uid = ExtractUserID($state);
# do stuff
if ($uid == 0) {

If the application is unable to extract the state information - say, due to a database timeout - then the $uid variable will not be explicitly set by the programmer. This will cause $uid to be regarded as equivalent to "0" in the conditional, allowing the original user to perform administrator actions. Even if the attacker cannot directly influence the state data, unexpected errors could cause incorrect privileges to be assigned to a user just by accident.

Example 3

The following code intends to concatenate a string to a variable and print the string.

(Bad Code)
Example Language:
char str[20];
strcat(str, "hello world");
printf("%s", str);

This might seem innocent enough, but str was not initialized, so it contains random memory. As a result, str[0] might not contain the null terminator, so the copy might start at an offset other than 0. The consequences can vary, depending on the underlying memory.

If a null terminator is found before str[8], then some bytes of random garbage will be printed before the "hello world" string. The memory might contain sensitive information from previous uses, such as a password (which might occur as a result of CWE-14 or CWE-244). In this example, it might not be a big deal, but consider what could happen if large amounts of memory are printed out before the null terminator is found.

If a null terminator isn't found before str[8], then a buffer overflow could occur, since strcat will first look for the null terminator, then copy 12 bytes starting with that location. Alternately, a buffer over-read might occur (CWE-126) if a null terminator isn't found before the end of the memory segment is reached, leading to a segmentation fault and crash.

+ Observed Examples
chain: an invalid value prevents a library file from being included, skipping initialization of key variables, leading to resultant eval injection.
Improper error checking in protection mechanism produces an uninitialized variable, allowing security bypass and code execution.
Use of uninitialized memory may allow code execution.
Free of an uninitialized pointer leads to crash and possible code execution.
OS kernel does not reset a port when starting a setuid program, allowing local users to access the port and gain privileges.
Product does not clear memory contents when generating an error message, leading to information leak.
Lack of initialization triggers NULL pointer dereference or double-free.
Uninitialized variable leads to code execution in popular desktop application.
chain: Uninitialized variable leads to infinite loop.
chain: Improper initialization leads to memory corruption.
Composite: race condition allows attacker to modify an object while it is still being initialized, causing software to access uninitialized memory.
Permission bitmap is not properly initialized, leading to resultant privilege elevation or DoS.
chain: game server can access player data structures before initialization has happened leading to NULL dereference
chain: uninitialized function pointers can be dereferenced allowing code execution
chain: improper initialization of memory can lead to NULL dereference
chain: some unprivileged ioctls do not verify that a structure has been initialized before invocation, leading to NULL dereference
+ 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, in Java, if the programmer does not explicitly initialize a variable, then the code could produce a compile-time error (if the variable is local) or automatically initialize the variable to the default value for the variable's type. In Perl, if explicit initialization is not performed, then a default value of undef is assigned, which is interpreted as 0, false, or an equivalent value depending on the context in which the variable is accessed.

Phase: Architecture and Design

Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values.

Phase: Implementation

Explicitly initialize all your variables and other data stores, either during declaration or just before the first usage.

Phase: Implementation

Pay close attention to complex conditionals that affect initialization, since some conditions might not perform the initialization.

Phase: Implementation

Avoid race conditions (CWE-362) during initialization routines.

Phase: Build and Compilation

Run or compile your software with settings that generate warnings about uninitialized variables or data.

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.

+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
(where the weakness is typically related to the presence of some other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory452Initialization and Cleanup Errors
Development Concepts (primary)699
ChildOfWeakness ClassWeakness Class664Improper Control of a Resource Through its Lifetime
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfCategoryCategory740CERT C Secure Coding Section 06 - Arrays (ARR)
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
ChildOfCategoryCategory7522009 Top 25 - Risky Resource Management
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfCategoryCategory846CERT Java Secure Coding Section 01 - Declarations and Initialization (DCL)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory874CERT C++ Secure Coding Section 06 - Arrays and the STL (ARR)
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
ChildOfCategoryCategory962SFP Secondary Cluster: Unchecked Status Condition
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness BaseWeakness Base453Insecure Default Variable Initialization
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base454External Initialization of Trusted Variables or Data Stores
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base455Non-exit on Failed Initialization
Research Concepts1000
ParentOfWeakness VariantWeakness Variant457Use of Uninitialized Variable
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base770Allocation of Resources Without Limits or Throttling
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base909Missing Initialization of Resource
Research Concepts (primary)1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERIncorrect initialization
CERT C Secure CodingARR02-CExplicitly specify array bounds, even if implicitly defined by an initializer
CERT C Secure CodingMEM09-CDo not assume memory allocation routines initialize memory
CERT Java Secure CodingDCL00-JPrevent class initialization cycles
CERT C++ Secure CodingARR02-CPPExplicitly specify array bounds, even if implicitly defined by an initializer
CERT C++ Secure CodingMEM09-CPPDo not assume memory allocation routines initialize memory
Software Fault PatternsSFP4Unchecked Status Condition
+ References
mercy. "Exploiting Uninitialized Data". Jan 2006. <>.
Microsoft Security Vulnerability Research & Defense. "MS08-014 : The Case of the Uninitialized Stack Variable Vulnerability". 2008-03-11. <>.
[REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 7, "Variable Initialization", Page 312.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modification DateModifierOrganizationSource
2008-07-01Sean EidemillerCigitalExternal
added/updated demonstrative examples
2008-07-01Eric DalciCigitalExternal
updated Potential_Mitigations, Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2009-01-12CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Description, Likelihood_of_Exploit, Modes_of_Introduction, Name, Observed_Examples, Potential_Mitigations, References, Relationships, Weakness_Ordinalities
2009-03-10CWE Content TeamMITREInternal
updated Potential_Mitigations
2009-05-27CWE Content TeamMITREInternal
updated Description, Relationships
2009-07-27CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2009-10-29CWE Content TeamMITREInternal
updated Common_Consequences
2010-02-16CWE Content TeamMITREInternal
updated Potential_Mitigations
2010-04-05CWE Content TeamMITREInternal
updated Applicable_Platforms
2010-06-21CWE Content TeamMITREInternal
updated Detection_Factors, Potential_Mitigations
2010-09-27CWE Content TeamMITREInternal
updated Observed_Examples
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011-09-13CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings
2013-02-21CWE Content TeamMITREInternal
updated Demonstrative_Examples, Relationships
2014-07-30CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITREInternal
updated Relationships
2017-01-19CWE Content TeamMITREInternal
updated Type
Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Incorrect or Incomplete Initialization

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Page Last Updated: January 18, 2017