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CWE-190: Integer Overflow or Wraparound

 
Integer Overflow or Wraparound
Weakness ID: 190 (Weakness Base)Status: Incomplete
+ Description

Description Summary

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.

+ Terminology Notes

"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.

+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

Language-independent

+ Common Consequences
ScopeEffect

Technical Impact: DoS: crash / exit / 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.

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.

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

+ 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.

+ Demonstrative Examples

Example 1

The following image processing code allocates a table for images.

(Bad Code)
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 Code)
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 Code)
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 Code)
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 Code)
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.
+ 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++). [R.190.5]

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. [R.190.3]

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.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)Named Chain(s) this relationship pertains toChain(s)
ChildOfWeakness ClassWeakness Class20Improper Input Validation
Seven Pernicious Kingdoms (primary)700
ChildOfCategoryCategory189Numeric Errors
Development Concepts699
ChildOfWeakness ClassWeakness Class682Incorrect Calculation
Development Concepts (primary)699
Research Concepts (primary)1000
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
ChildOfCategoryCategory8022010 Top 25 - Risky Resource Management
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory8652011 Top 25 - Risky Resource Management
Weaknesses in the 2011 CWE/SANS Top 25 Most Dangerous Software Errors (primary)900
ChildOfCategoryCategory872CERT C++ Secure Coding Section 04 - Integers (INT)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory876CERT C++ Secure Coding Section 08 - Memory Management (MEM)
Weaknesses Addressed by the CERT C++ Secure Coding Standard868
ChildOfCategoryCategory885SFP Cluster: Risky Values
Software Fault Pattern (SFP) Clusters (primary)888
CanPrecedeWeakness ClassWeakness Class119Improper Restriction of Operations within the Bounds of a Memory Buffer
Research Concepts1000
Integer Overflow to Buffer Overflow680
StartsChainCompound Element: ChainCompound Element: Chain680Integer Overflow to Buffer Overflow
Named Chains709
Integer Overflow to Buffer Overflow680
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
PeerOfWeakness BaseWeakness Base128Wrap-around Error
Research Concepts1000
+ Relationship Notes

Integer overflows can be primary to buffer overflows.

+ Functional Areas
  • Number processing
  • Memory management
  • Non-specific, counters
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERInteger overflow (wrap or wraparound)
7 Pernicious KingdomsInteger Overflow
CLASPInteger overflow
CERT C Secure CodingINT03-CUse a secure integer library
CERT C Secure CodingINT30-CEnsure that unsigned integer operations do not wrap
CERT C Secure CodingINT32-CEnsure 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-CEnsure that the arguments to calloc(), when multiplied, can be represented as a size_t
CERT C Secure CodingMEM35-CAllocate sufficient memory for an object
WASC3Integer Overflows
CERT C++ Secure CodingINT03-CPPUse a secure integer library
CERT C++ Secure CodingINT30-CPPEnsure that unsigned integer operations do not wrap
CERT C++ Secure CodingINT32-CPPEnsure that operations on signed integers do not result in overflow
CERT C++ Secure CodingINT35-CPPEvaluate integer expressions in a larger size before comparing or assigning to that size
CERT C++ Secure CodingMEM07-CPPEnsure that the arguments to calloc(), when multiplied, can be represented as a size_t
CERT C++ Secure CodingMEM35-CPPAllocate sufficient memory for an object
+ References
[R.190.1] Yves Younan. "An overview of common programming security vulnerabilities and possible solutions". Student thesis section 5.4.3. August 2003. <http://fort-knox.org/thesis.pdf>.
[R.190.2] blexim. "Basic Integer Overflows". Phrack - Issue 60, Chapter 10. <http://www.phrack.org/issues.html?issue=60&id=10#article>.
[R.190.3] [REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 20, "Integer Overflows" Page 620. 2nd Edition. Microsoft. 2002.
[R.190.4] [REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 7: Integer Overflows." Page 119. McGraw-Hill. 2010.
[R.190.5] [REF-18] David LeBlanc and Niels Dekker. "SafeInt". <http://safeint.codeplex.com/>.
[R.190.6] 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-7] 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
Externally Mined
Modifications
Modification DateModifierOrganizationSource
2008-09-08MITREInternal
updated Common_Consequences, Relationships, Relationship_Notes, Taxonomy_Mappings, Terminology_Notes
2008-10-14MITREInternal
updated Common_Consequences, Description, Potential_Mitigations, Terminology_Notes
2008-11-24MITREInternal
updated Relationships, Taxonomy_Mappings
2009-01-12MITREInternal
updated Description, Name
2009-05-27MITREInternal
updated Demonstrative_Examples
2009-10-29MITREInternal
updated Relationships
2010-02-16MITREInternal
updated Applicable_Platforms, Detection_Factors, Functional_Areas, Observed_Examples, Potential_Mitigations, References, Related_Attack_Patterns, Relationships, Taxonomy_Mappings, Terminology_Notes
2010-04-05MITREInternal
updated Demonstrative_Examples, Detection_Factors, Potential_Mitigations, References, Related_Attack_Patterns
2010-06-21MITREInternal
updated Common_Consequences, Potential_Mitigations, References
2010-09-27MITREInternal
updated Observed_Examples, Potential_Mitigations
2011-06-01MITREInternal
updated Common_Consequences
2011-06-27MITREInternal
updated Relationships
2011-09-13MITREInternal
updated Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2012-05-11MITREInternal
updated Common_Consequences, Demonstrative_Examples, References, Relationships
2012-10-30MITREInternal
updated Potential_Mitigations
2013-07-17MITREInternal
updated References
Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Integer Overflow (Wrap or Wraparound)
Page Last Updated: June 23, 2014