Numeric Truncation Error
Weakness ID: 197 (Weakness Base)Status: Incomplete
+ Description

Description Summary

Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.

Extended Description

When a primitive is cast to a smaller primitive, the high order bits of the large value are lost in the conversion, potentially resulting in an unexpected value that is not equal to the original value. This value may be required as an index into a buffer, a loop iterator, or simply necessary state data. In any case, the value cannot be trusted and the system will be in an undefined state. While this method may be employed viably to isolate the low bits of a value, this usage is rare, and truncation usually implies that an implementation error has occurred.

+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

C

C++

Java

.NET

+ Common Consequences
ScopeEffect
Integrity

The true value of the data is lost and corrupted data is used.

+ Likelihood of Exploit

Low

+ Demonstrative Examples

Example 1

This example, while not exploitable, shows the possible mangling of values associated with truncation errors:

Example Language: C 
#include <stdio.h>
int main() {
int intPrimitive;
short shortPrimitive;
intPrimitive = (int)(~((int)0) ^ (1 << (sizeof(int)*8-1)));
shortPrimitive = intPrimitive;
printf("Int MAXINT: %d\nShort MAXINT: %d\n",
intPrimitive, shortPrimitive);
return (0);
}

The above code, when compiled and run, returns the following output: Int MAXINT: 2147483647 Short MAXINT: -1 A frequent paradigm for such a problem being exploitable is when the truncated value is used as an array index, which can happen implicitly when 64-bit values are used as indexes, as they are truncated to 32 bits.

+ Observed Examples
ReferenceDescription
CVE-2009-0231Integer truncation of length value leads to heap-based buffer overflow.
CVE-2008-3282Size of a particular type changes for 64-bit platforms, leading to an integer truncation in document processor causes incorrect index to be generated.
+ Potential Mitigations

Phase: Implementation

Ensure that no casts, implicit or explicit, take place that move from a larger size primitive or a smaller size primitive.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base681Incorrect Conversion between Numeric Types
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
CanAlsoBeCategoryCategory192Integer Coercion Error
Research Concepts1000
CanAlsoBeWeakness BaseWeakness Base194Unexpected Sign Extension
Research Concepts1000
CanAlsoBeWeakness VariantWeakness Variant195Signed to Unsigned Conversion Error
Research Concepts1000
CanAlsoBeWeakness VariantWeakness Variant196Unsigned to Signed Conversion Error
Research Concepts1000
+ Research Gaps

This weakness has traditionally been under-studied and under-reported, although vulnerabilities in popular software have been published in 2008 and 2009.

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERNumeric truncation error
CLASPTruncation error
CERT C Secure CodingINT02-CUnderstand integer conversion rules
CERT C Secure CodingINT05-CDo not use input functions to convert character data if they cannot handle all possible inputs
CERT C Secure CodingINT31-CEnsure that integer conversions do not result in lost or misinterpreted data
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Applicable Platforms, Common Consequences, Relationships, Other Notes, Taxonomy Mappings
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy Mappings
2009-05-27CWE Content TeamMITREInternal
updated Demonstrative Examples
2009-07-27CWE Content TeamMITREInternal
updated Description, Observed Examples, Other Notes, Research Gaps
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