CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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ID

CWE-190: Integer Overflow or Wraparound

Weakness ID: 190
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control.
+ Extended Description
An integer overflow or wraparound occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may wrap to become a very small or negative number. While this may be intended behavior in circumstances that rely on wrapping, it can have security consequences if the wrap is unexpected. This is especially the case if the integer overflow can be triggered using user-supplied inputs. This becomes security-critical when the result is used to control looping, make a security decision, or determine the offset or size in behaviors such as memory allocation, copying, concatenation, etc.
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
+ Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
NatureTypeIDName
ChildOfClassClass682Incorrect Calculation
+ Relevant to the view "Development Concepts" (CWE-699)
NatureTypeIDName
ChildOfClassClass682Incorrect Calculation
+ Relevant to the view "Seven Pernicious Kingdoms" (CWE-700)
NatureTypeIDName
ChildOfClassClass20Improper Input Validation
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

PhaseNote
Implementation
+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

(Language-Independent classes): (Undetermined Prevalence)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

ScopeImpactLikelihood
Availability

Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Instability

This weakness will generally lead to undefined behavior and therefore crashes. In the case of overflows involving loop index variables, the likelihood of infinite loops is also high.
Integrity

Technical Impact: Modify Memory

If the value in question is important to data (as opposed to flow), simple data corruption has occurred. Also, if the wrap around results in other conditions such as buffer overflows, further memory corruption may occur.
Confidentiality
Availability
Access Control

Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism

This weakness can sometimes trigger buffer overflows which can be used to execute arbitrary code. This is usually outside the scope of a program's implicit security policy.
+ Likelihood Of Exploit
Medium
+ Demonstrative Examples

Example 1

The following image processing code allocates a table for images.

(bad)
Example Language:
img_t table_ptr; /*struct containing img data, 10kB each*/
int num_imgs;
...
num_imgs = get_num_imgs();
table_ptr = (img_t*)malloc(sizeof(img_t)*num_imgs);
...

This code intends to allocate a table of size num_imgs, however as num_imgs grows large, the calculation determining the size of the list will eventually overflow (CWE-190). This will result in a very small list to be allocated instead. If the subsequent code operates on the list as if it were num_imgs long, it may result in many types of out-of-bounds problems (CWE-119).

Example 2

The following code excerpt from OpenSSH 3.3 demonstrates a classic case of integer overflow:

(bad)
Example Language:
nresp = packet_get_int();
if (nresp > 0) {
response = xmalloc(nresp*sizeof(char*));
for (i = 0; i < nresp; i++) response[i] = packet_get_string(NULL);

}

If nresp has the value 1073741824 and sizeof(char*) has its typical value of 4, then the result of the operation nresp*sizeof(char*) overflows, and the argument to xmalloc() will be 0. Most malloc() implementations will happily allocate a 0-byte buffer, causing the subsequent loop iterations to overflow the heap buffer response.

Example 3

Integer overflows can be complicated and difficult to detect. The following example is an attempt to show how an integer overflow may lead to undefined looping behavior:

(bad)
Example Language:
short int bytesRec = 0;
char buf[SOMEBIGNUM];

while(bytesRec < MAXGET) {
bytesRec += getFromInput(buf+bytesRec);

}

In the above case, it is entirely possible that bytesRec may overflow, continuously creating a lower number than MAXGET and also overwriting the first MAXGET-1 bytes of buf.

Example 4

In this example the method determineFirstQuarterRevenue is used to determine the first quarter revenue for an accounting/business application. The method retrieves the monthly sales totals for the first three months of the year, calculates the first quarter sales totals from the monthly sales totals, calculates the first quarter revenue based on the first quarter sales, and finally saves the first quarter revenue results to the database.

(bad)
Example Language:
#define JAN 1
#define FEB 2
#define MAR 3

short getMonthlySales(int month) {...}

float calculateRevenueForQuarter(short quarterSold) {...}

int determineFirstQuarterRevenue() {
// Variable for sales revenue for the quarter

float quarterRevenue = 0.0f;

short JanSold = getMonthlySales(JAN); /* Get sales in January */
short FebSold = getMonthlySales(FEB); /* Get sales in February */
short MarSold = getMonthlySales(MAR); /* Get sales in March */
// Calculate quarterly total

short quarterSold = JanSold + FebSold + MarSold;
// Calculate the total revenue for the quarter

quarterRevenue = calculateRevenueForQuarter(quarterSold);

saveFirstQuarterRevenue(quarterRevenue);

return 0;

}

However, in this example the primitive type short int is used for both the monthly and the quarterly sales variables. In C the short int primitive type has a maximum value of 32768. This creates a potential integer overflow if the value for the three monthly sales adds up to more than the maximum value for the short int primitive type. An integer overflow can lead to data corruption, unexpected behavior, infinite loops and system crashes. To correct the situation the appropriate primitive type should be used, as in the example below, and/or provide some validation mechanism to ensure that the maximum value for the primitive type is not exceeded.

(good)
Example Language:
...
float calculateRevenueForQuarter(long quarterSold) {...}

int determineFirstQuarterRevenue() {
...
// Calculate quarterly total

long quarterSold = JanSold + FebSold + MarSold;
// Calculate the total revenue for the quarter

quarterRevenue = calculateRevenueForQuarter(quarterSold);

...

}

Note that an integer overflow could also occur if the quarterSold variable has a primitive type long but the method calculateRevenueForQuarter has a parameter of type short.

+ Observed Examples
ReferenceDescription
chain: integer overflow leads to use-after-free
Integer overflow via a large number of arguments.
Integer overflow in OpenSSH as listed in the demonstrative examples.
Image with large width and height leads to integer overflow.
Length value of -1 leads to allocation of 0 bytes and resultant heap overflow.
Length value of -1 leads to allocation of 0 bytes and resultant heap overflow.
chain: unchecked message size metadata allows integer overflow (CWE-190) leading to buffer overflow (CWE-119).
+ Potential Mitigations

Phase: Requirements

Ensure that all protocols are strictly defined, such that all out-of-bounds behavior can be identified simply, and require strict conformance to the protocol.

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. If possible, choose a language or compiler that performs automatic bounds checking.

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. Use libraries or frameworks that make it easier to handle numbers without unexpected consequences. Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]

Phase: Implementation

Strategy: Input Validation

Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range. Use unsigned integers where possible. This makes it easier to perform sanity checks for integer overflows. When signed integers are required, ensure that the range check includes minimum values as well as maximum values.

Phase: Implementation

Understand the programming language's underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, "not-a-number" calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-112] Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.

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: Compilation or Build Hardening

Examine compiler warnings closely and eliminate problems with potential security implications, such as signed / unsigned mismatch in memory operations, or use of uninitialized variables. Even if the weakness is rarely exploitable, a single failure may lead to the compromise of the entire system.
+ 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.

Effectiveness: High

Black Box

Sometimes, evidence of 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

Without visibility into the code, black box methods may not be able to sufficiently distinguish this weakness from others, requiring follow-up manual methods to diagnose the underlying problem.

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 static analysis is useful for evaluating the correctness of allocation calculations. This can be useful for detecting overflow conditions (CWE-190) or similar weaknesses that might have serious security impacts on the program.

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 - Binary or 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: 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:

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:

Highly cost effective:
  • Source code Weakness Analyzer
  • Context-configured Source Code Weakness Analyzer

Effectiveness: High

Architecture or 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: High

+ Functional Areas
  • Number Processing
  • Memory Management
  • Counters
+ Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
+ Notes

Relationship

Integer overflows can be primary to buffer overflows.

Terminology

"Integer overflow" is sometimes used to cover several types of errors, including signedness errors, or buffer overflows that involve manipulation of integer data types instead of characters. Part of the confusion results from the fact that 0xffffffff is -1 in a signed context. Other confusion also arises because of the role that integer overflows have in chains.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERInteger overflow (wrap or wraparound)
7 Pernicious KingdomsInteger Overflow
CLASPInteger overflow
CERT C Secure CodingINT18-CCWE More AbstractEvaluate integer expressions in a larger size before comparing or assigning to that size
CERT C Secure CodingINT30-CCWE More AbstractEnsure that unsigned integer operations do not wrap
CERT C Secure CodingINT32-CImpreciseEnsure that operations on signed integers do not result in overflow
CERT C Secure CodingINT35-CEvaluate integer expressions in a larger size before comparing or assigning to that size
CERT C Secure CodingMEM07-CCWE More AbstractEnsure that the arguments to calloc(), when multiplied, do not wrap
CERT C Secure CodingMEM35-CAllocate sufficient memory for an object
WASC3Integer Overflows
Software Fault PatternsSFP1Glitch in computation
+ References
[REF-145] Yves Younan. "An overview of common programming security vulnerabilities and possible solutions". Student thesis section 5.4.3. 2003-08. <http://fort-knox.org/thesis.pdf>.
[REF-146] blexim. "Basic Integer Overflows". Phrack - Issue 60, Chapter 10. <http://www.phrack.org/issues.html?issue=60&id=10#article>.
[REF-112] Michael Howard and David LeBlanc. "Writing Secure Code". Chapter 20, "Integer Overflows" Page 620. 2nd Edition. Microsoft. 2002.
[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 7: Integer Overflows." Page 119. McGraw-Hill. 2010.
[REF-106] David LeBlanc and Niels Dekker. "SafeInt". <http://safeint.codeplex.com/>.
[REF-150] Johannes Ullrich. "Top 25 Series - Rank 17 - Integer Overflow Or Wraparound". SANS Software Security Institute. 2010-03-18. <http://software-security.sans.org/blog/2010/03/18/top-25-series-rank-17-integer-overflow-or-wraparound>.
[REF-62] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 6, "Signed Integer Boundaries", Page 220.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVER
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITRE
updated Common_Consequences, Relationships, Relationship_Notes, Taxonomy_Mappings, Terminology_Notes
2008-10-14CWE Content TeamMITRE
updated Common_Consequences, Description, Potential_Mitigations, Terminology_Notes
2008-11-24CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2009-01-12CWE Content TeamMITRE
updated Description, Name
2009-05-27CWE Content TeamMITRE
updated Demonstrative_Examples
2009-10-29CWE Content TeamMITRE
updated Relationships
2010-02-16CWE Content TeamMITRE
updated Applicable_Platforms, Detection_Factors, Functional_Areas, Observed_Examples, Potential_Mitigations, References, Related_Attack_Patterns, Relationships, Taxonomy_Mappings, Terminology_Notes
2010-04-05CWE Content TeamMITRE
updated Demonstrative_Examples, Detection_Factors, Potential_Mitigations, References, Related_Attack_Patterns
2010-06-21CWE Content TeamMITRE
updated Common_Consequences, Potential_Mitigations, References
2010-09-27CWE Content TeamMITRE
updated Observed_Examples, Potential_Mitigations
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2011-06-27CWE Content TeamMITRE
updated Relationships
2011-09-13CWE Content TeamMITRE
updated Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Common_Consequences, Demonstrative_Examples, References, Relationships
2012-10-30CWE Content TeamMITRE
updated Potential_Mitigations
2013-07-17CWE Content TeamMITRE
updated References
2014-07-30CWE Content TeamMITRE
updated Detection_Factors, Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITRE
updated Relationships
2017-01-19CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Functional_Areas, Observed_Examples, References, Taxonomy_Mappings
Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Integer Overflow (Wrap or Wraparound)

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Page Last Updated: November 14, 2017