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-681: Incorrect Conversion between Numeric Types

Weakness ID: 681
Abstraction: Class
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
When converting from one data type to another, such as long to integer, data can be omitted or translated in a way that produces unexpected values. If the resulting values are used in a sensitive context, then dangerous behaviors may occur.
+ 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)
NatureTypeIDName
ChildOfClassClass704Incorrect Type Conversion or Cast
ParentOfClassClass192Integer Coercion Error
ParentOfBaseBase194Unexpected Sign Extension
ParentOfVariantVariant195Signed to Unsigned Conversion Error
ParentOfVariantVariant196Unsigned to Signed Conversion Error
ParentOfBaseBase197Numeric Truncation Error
CanPrecedeClassClass682Incorrect Calculation
+ Relevant to the view "Development Concepts" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory136Type Errors
MemberOfCategoryCategory189Numeric Errors
ParentOfBaseBase194Unexpected Sign Extension
ParentOfVariantVariant195Signed to Unsigned Conversion Error
ParentOfVariantVariant196Unsigned to Signed Conversion Error
ParentOfBaseBase197Numeric Truncation Error
+ 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
Other
Integrity

Technical Impact: Unexpected State; Quality Degradation

The program could wind up using the wrong number and generate incorrect results. If the number is used to allocate resources or make a security decision, then this could introduce a vulnerability.
+ Likelihood Of Exploit
High
+ Demonstrative Examples

Example 1

In the following Java example, a float literal is cast to an integer, thus causing a loss of precision.

(bad)
Example Language: Java 
int i = (int) 33457.8f;

Example 2

This code adds a float and an integer together, casting the result to an integer.

(bad)
Example Language: PHP 
$floatVal = 1.8345;
$intVal = 3;
$result = (int)$floatVal + $intVal;

Normally, PHP will preserve the precision of this operation, making $result = 4.8345. After the cast to int, it is reasonable to expect PHP to follow rounding convention and set $result = 5. However, the explicit cast to int always rounds DOWN, so the final value of $result is 4. This behavior may have unintended consequences.

Example 3

In this example the variable amount can hold a negative value when it is returned. Because the function is declared to return an unsigned int, amount will be implicitly converted to unsigned.

(bad)
Example Language:
unsigned int readdata () {
int amount = 0;
...
if (result == ERROR)
amount = -1;
...
return amount;

}

If the error condition in the code above is met, then the return value of readdata() will be 4,294,967,295 on a system that uses 32-bit integers.

Example 4

In this example, depending on the return value of accecssmainframe(), the variable amount can hold a negative value when it is returned. Because the function is declared to return an unsigned value, amount will be implicitly cast to an unsigned number.

(bad)
Example Language:
unsigned int readdata () {
int amount = 0;
...
amount = accessmainframe();
...
return amount;

}

If the return value of accessmainframe() is -1, then the return value of readdata() will be 4,294,967,295 on a system that uses 32-bit integers.

+ Observed Examples
ReferenceDescription
Chain: integer signedness error (CWE-195) passes signed comparison, leading to heap overflow (CWE-122)
Chain: signed short width value in image processor is sign extended during conversion to unsigned int, which leads to integer overflow and heap-based buffer overflow.
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

Avoid making conversion between numeric types. Always check for the allowed ranges.
+ 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.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CERT C Secure CodingFLP34-CCWE More AbstractEnsure that floating point conversions are within range of the new type
CERT C Secure CodingINT15-CUse intmax_t or uintmax_t for formatted IO on programmer-defined integer types
CERT C Secure CodingINT31-CCWE More AbstractEnsure that integer conversions do not result in lost or misinterpreted data
CERT C Secure CodingINT35-CEvaluate integer expressions in a larger size before comparing or assigning to that size
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, "Type Conversions", Page 223.. 1st Edition. Addison Wesley. 2006.
+ Content History
Modifications
Modification DateModifierOrganizationSource
2008-07-01Sean EidemillerCigital
added/updated demonstrative examples
2008-07-01Eric DalciCigital
updated Potential_Mitigations, Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Relationships
2008-11-24CWE Content TeamMITRE
updated Description, Relationships, Taxonomy_Mappings
2009-12-28CWE Content TeamMITRE
updated Applicable_Platforms, Likelihood_of_Exploit, Potential_Mitigations
2010-02-16CWE Content TeamMITRE
updated Relationships
2011-03-29CWE Content TeamMITRE
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011-06-27CWE Content TeamMITRE
updated Common_Consequences, Observed_Examples, Relationships
2011-09-13CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2017-11-08CWE Content TeamMITRE
updated Likelihood_of_Exploit, Observed_Examples, Taxonomy_Mappings, Type

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Page Last Updated: November 14, 2017