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-197: Numeric Truncation Error

Weakness ID: 197
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
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.
+ 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 "Development Concepts" (CWE-699)
NatureTypeIDName
ChildOfClassClass681Incorrect Conversion between Numeric Types
+ 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

C: (Undetermined Prevalence)

C++: (Undetermined Prevalence)

Java: (Undetermined Prevalence)

C#: (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
Integrity

Technical Impact: Modify Memory

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:

(bad)
Example Language:
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);

The above code, when compiled and run on certain systems, returns the following output:

(result)
 
Int MAXINT: 2147483647
Short MAXINT: -1

This problem may be exploitable 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.

Example 2

In the following Java example, the method updateSalesForProduct is part of a business application class that updates the sales information for a particular product. The method receives as arguments the product ID and the integer amount sold. The product ID is used to retrieve the total product count from an inventory object which returns the count as an integer. Before calling the method of the sales object to update the sales count the integer values are converted to The primitive type short since the method requires short type for the method arguments.

(bad)
Example Language: Java 
...
// update sales database for number of product sold with product ID

public void updateSalesForProduct(String productID, int amountSold) {
// get the total number of products in inventory database
int productCount = inventory.getProductCount(productID);
// convert integer values to short, the method for the
// sales object requires the parameters to be of type short

short count = (short) productCount;
short sold = (short) amountSold;
// update sales database for product

sales.updateSalesCount(productID, count, sold);

}
...

However, a numeric truncation error can occur if the integer values are higher than the maximum value allowed for the primitive type short. This can cause unexpected results or loss or corruption of data. In this case the sales database may be corrupted with incorrect data. Explicit casting from a from a larger size primitive type to a smaller size primitive type should be prevented. The following example an if statement is added to validate that the integer values less than the maximum value for the primitive type short before the explicit cast and the call to the sales method.

(good)
Example Language: Java 
...
// update sales database for number of product sold with product ID

public void updateSalesForProduct(String productID, int amountSold) {
// get the total number of products in inventory database
int productCount = inventory.getProductCount(productID);
// make sure that integer numbers are not greater than
// maximum value for type short before converting

if ((productCount < Short.MAX_VALUE) && (amountSold < Short.MAX_VALUE)) {
// convert integer values to short, the method for the
// sales object requires the parameters to be of type short
short count = (short) productCount;
short sold = (short) amountSold;
// update sales database for product

sales.updateSalesCount(productID, count, sold);

else {
// throw exception or perform other processing
...

}

}
...
+ Observed Examples
ReferenceDescription
Integer truncation of length value leads to heap-based buffer overflow.
Size 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.
+ 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

Research Gap

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 CodingFIO34-CCWE More AbstractDistinguish between characters read from a file and EOF or WEOF
CERT C Secure CodingFLP34-CCWE More AbstractEnsure that floating point conversions are within range of the new type
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-CCWE More AbstractEnsure that integer conversions do not result in lost or misinterpreted data
CERT Java Secure CodingNUM12-JEnsure conversions of numeric types to narrower types do not result in lost or misinterpreted data
Software Fault PatternsSFP1Glitch in computation
+ References
[REF-62] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 6, "Truncation", Page 259.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVER
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITRE
updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
2008-11-24CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2009-05-27CWE Content TeamMITRE
updated Demonstrative_Examples
2009-07-27CWE Content TeamMITRE
updated Description, Observed_Examples, Other_Notes, Research_Gaps
2010-12-13CWE Content TeamMITRE
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011-09-13CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated References, Relationships, Taxonomy_Mappings
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2017-11-08CWE Content TeamMITRE
updated Taxonomy_Mappings

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Page Last Updated: November 14, 2017