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.

Primary

Implementation

High

Other
Integrity
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.

Automated Static Analysis
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.)
High

Implementation
Avoid making conversion between numeric types. Always check for the allowed ranges.

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

int i = (int) 33457.8f;

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

$floatVal = 1.8345;$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.

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.

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.

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.

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.

CVE-2022-2639
Chain: integer coercion error (CWE-192) prevents a return value from indicating an error, leading to out-of-bounds write (CWE-787)
https://www.cve.org/CVERecord?id=CVE-2022-2639

CVE-2021-43537
Chain: in a web browser, an unsigned 64-bit integer is forcibly cast to a 32-bit integer (CWE-681) and potentially leading to an integer overflow (CWE-190). If an integer overflow occurs, this can cause heap memory corruption (CWE-122)
https://www.cve.org/CVERecord?id=CVE-2021-43537

CVE-2007-4268
Chain: integer signedness error (CWE-195) passes signed comparison, leading to heap overflow (CWE-122)
https://www.cve.org/CVERecord?id=CVE-2007-4268

CVE-2007-4988
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.
https://www.cve.org/CVERecord?id=CVE-2007-4988

CVE-2009-0231
Integer truncation of length value leads to heap-based buffer overflow.
https://www.cve.org/CVERecord?id=CVE-2009-0231

CVE-2008-3282
Size of a particular type changes for 64-bit platforms, leading to an integer truncation in document processor causes incorrect index to be generated.
https://www.cve.org/CVERecord?id=CVE-2008-3282

FLP34-C
Ensure that floating point conversions are within range of the new type
CWE More Abstract

INT15-C
Use intmax_t or uintmax_t for formatted IO on programmer-defined integer types

INT31-C
Ensure that integer conversions do not result in lost or misinterpreted data
CWE More Abstract

INT35-C
Evaluate integer expressions in a larger size before comparing or assigning to that size

NUM12-J
Ensure conversions of numeric types to narrower types do not result in lost or misinterpreted data

SFP1
Glitch in computation

ASCSM-CWE-681

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

CWE Community
2008-04-11
Draft 9
2008-04-11
Submitted by members of the CWE community to extend early CWE versions

Sean Eidemiller
Cigital
2008-07-01
added/updated demonstrative examples

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Relationships

CWE Content Team
MITRE
2008-11-24
updated Description, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2009-12-28
updated Applicable_Platforms, Likelihood_of_Exploit, Potential_Mitigations

CWE Content Team
MITRE
2010-02-16
updated Relationships

CWE Content Team
MITRE
2011-03-29
updated Demonstrative_Examples

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2011-06-27
updated Common_Consequences, Observed_Examples, Relationships

CWE Content Team
MITRE
2011-09-13
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-05-11
updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2014-07-30
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2017-11-08
updated Likelihood_of_Exploit, Observed_Examples, Taxonomy_Mappings, Type

CWE Content Team
MITRE
2019-01-03
updated References, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2019-06-20
updated Relationships, Type

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2020-08-20
updated Relationships

CWE Content Team
MITRE
2020-12-10
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated Relationships

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2023-10-26
updated Observed_Examples

CWE Content Team
MITRE
2024-02-29
4.14
2024-02-29
updated Observed_Examples

CWE Content Team
MITRE
2025-04-03
4.17
2025-04-03
updated Applicable_Platforms

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Detection_Factors, Weakness_Ordinalities