Numeric Truncation Error

Incomplete Base

Structure: Simple

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.

Common Consequences 1

Scope: Integrity

Impact: Modify Memory

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

Detection Methods 2

FuzzingHigh

Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.

Automated Static AnalysisHigh

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Potential Mitigations 1

Phase: Implementation

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

Demonstrative Examples 2

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

Code Example:Bad
C
c

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

Code Example:Result
bash

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.

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.

Code Example:

Bad

Java

java

// update sales database for number of product sold with product ID* public void updateSalesForProduct(String productID, int amountSold) { ```

java

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.

Code Example:

Good

Java

java

// update sales database for number of product sold with product ID* public void updateSalesForProduct(String productID, int amountSold) { ```

java

// convert integer values to short, the method for the*

java

Observed Examples 3

CVE-2020-17087Chain: integer truncation (Numeric Truncation Error) causes small buffer allocation (Incorrect Calculation of Buffer Size) leading to out-of-bounds write (Out-of-bounds Write) in kernel pool, as exploited in the wild per CISA KEV.

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.

References 1

The Art of Software Security Assessment

Mark Dowd, John McDonald, and Justin Schuh

Addison Wesley

2006

ID: REF-62

Likelihood of Exploit

Low

Applicable Platforms

Languages:

C : UndeterminedC++ : UndeterminedJava : UndeterminedC# : Undetermined

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Incorrect Conversion between Numeric Types (CWE-681)

ChildOf:

Incorrect Conversion between Numeric Types (CWE-681)

ChildOf:

Incorrect Conversion between Numeric Types (CWE-681)

CanAlsoBe:

Signed to Unsigned Conversion Error (CWE-195)

CanAlsoBe:

Unsigned to Signed Conversion Error (CWE-196)

CanAlsoBe:

Integer Coercion Error (CWE-192)

CanAlsoBe:

Unexpected Sign Extension (CWE-194)

Taxonomy Mapping

PLOVER
CLASP
CERT C Secure Coding
CERT C Secure Coding
CERT C Secure Coding
CERT C Secure Coding
CERT C Secure Coding
The CERT Oracle Secure Coding Standard for Java (2011)
Software Fault Patterns

Notes

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