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CWE-197: Numeric Truncation Error

 
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

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 Code)
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 Code)
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 Code)
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.

+ 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
ChildOfCategoryCategory848CERT Java Secure Coding Section 03 - Numeric Types and Operations (NUM)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory872CERT C++ Secure Coding Section 04 - Integers (INT)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory885SFP Cluster: Risky Values
Software Fault Pattern (SFP) Clusters (primary)888
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
CERT Java Secure CodingNUM12-JEnsure conversions of numeric types to narrower types do not result in lost or misinterpreted data
CERT C++ Secure CodingINT02-CPPUnderstand integer conversion rules
CERT C++ Secure CodingINT05-CPPDo not use input functions to convert character data if they cannot handle all possible inputs
CERT C++ Secure CodingINT31-CPPEnsure that integer conversions do not result in lost or misinterpreted data
+ References
[REF-7] 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
Externally Mined
Modifications
Modification DateModifierOrganizationSource
2008-09-08MITREInternal
updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
2008-11-24MITREInternal
updated Relationships, Taxonomy_Mappings
2009-05-27MITREInternal
updated Demonstrative_Examples
2009-07-27MITREInternal
updated Description, Observed_Examples, Other_Notes, Research_Gaps
2010-12-13MITREInternal
updated Demonstrative_Examples
2011-06-01MITREInternal
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011-09-13MITREInternal
updated Relationships, Taxonomy_Mappings
2012-05-11MITREInternal
updated References, Relationships, Taxonomy_Mappings
Page Last Updated: June 23, 2014