A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().

Primary

Heap Overflow

Heap Buffer Overflow

Implementation

High

Availability
DoS: Crash, Exit, or Restart
DoS: Resource Consumption (CPU)
DoS: Resource Consumption (Memory)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.

Integrity
Confidentiality
Availability
Access Control
Execute Unauthorized Code or Commands
Bypass Protection Mechanism
Modify Memory
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy. Besides important user data, heap-based overflows can be used to overwrite function pointers that may be living in memory, pointing it to the attacker's code. Even in applications that do not explicitly use function pointers, the run-time will usually leave many in memory. For example, object methods in C++ are generally implemented using function pointers. Even in C programs, there is often a global offset table used by the underlying runtime.

Integrity
Confidentiality
Availability
Access Control
Other
Execute Unauthorized Code or Commands
Bypass Protection Mechanism
Other
When the consequence is arbitrary code execution, this can often be used to subvert any other security service.

Fuzzing
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.
High

Automated Dynamic Analysis
Use tools that are integrated during
compilation to insert runtime error-checking mechanisms
related to memory safety errors, such as AddressSanitizer
(ASan) for C/C++ [REF-1518].
Moderate
Crafted inputs are necessary to
reach the code containing the error, such as generated
by fuzzers. Also, these tools may reduce performance,
and they only report the error condition - not the
original mistake that led to the
error.

Pre-design: Use a language or compiler that performs automatic bounds checking.

Architecture and Design
Use an abstraction library to abstract away risky APIs. Not a complete solution.

Operation
Build and Compilation
Environment Hardening

Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.
D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.

Defense in Depth

This is not necessarily a complete solution, since these mechanisms only detect certain types of overflows. In addition, the result is still a denial of service, since the typical response is to exit the application.

Operation
Build and Compilation
Environment Hardening

Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.
Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.
For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

Defense in Depth
These techniques do not provide a complete solution. For instance, exploits frequently use a bug that discloses memory addresses in order to maximize reliability of code execution [REF-1337]. It has also been shown that a side-channel attack can bypass ASLR [REF-1333].

Implementation
Implement and perform bounds checking on input.

Implementation
Libraries or Frameworks
Do not use dangerous functions such as gets. Look for their safe equivalent, which checks for the boundary.

Operation
Use OS-level preventative functionality. This is not a complete solution, but it provides some defense in depth.

While buffer overflow examples can be rather complex, it is possible to have very simple, yet still exploitable, heap-based buffer overflows:

#define BUFSIZE 256int main(int argc, char **argv) {char *buf;buf = (char *)malloc(sizeof(char)*BUFSIZE);strcpy(buf, argv[1]);}

The buffer is allocated heap memory with a fixed size, but there is no guarantee the string in argv[1] will not exceed this size and cause an overflow.

This example applies an encoding procedure to an input string and stores it into a buffer.

char * copy_input(char *user_supplied_string){
int i, dst_index;char *dst_buf = (char*)malloc(4*sizeof(char) * MAX_SIZE);if ( MAX_SIZE <= strlen(user_supplied_string) ){die("user string too long, die evil hacker!");}dst_index = 0;for ( i = 0; i < strlen(user_supplied_string); i++ ){
if( '&' == user_supplied_string[i] ){dst_buf[dst_index++] = '&';dst_buf[dst_index++] = 'a';dst_buf[dst_index++] = 'm';dst_buf[dst_index++] = 'p';dst_buf[dst_index++] = ';';}else if ('<' == user_supplied_string[i] ){

/* encode to &lt; */

}else dst_buf[dst_index++] = user_supplied_string[i];
}return dst_buf;
}

The programmer attempts to encode the ampersand character in the user-controlled string, however the length of the string is validated before the encoding procedure is applied. Furthermore, the programmer assumes encoding expansion will only expand a given character by a factor of 4, while the encoding of the ampersand expands by 5. As a result, when the encoding procedure expands the string it is possible to overflow the destination buffer if the attacker provides a string of many ampersands.

CVE-2025-46687
Chain: Javascript engine code does not perform a length check (CWE-1284) leading to integer overflow (CWE-190) causing allocation of smaller buffer than expected (CWE-131) resulting in a heap-based buffer overflow (CWE-122)
https://www.cve.org/CVERecord?id=CVE-2025-46687

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-2009-2523
Chain: product does not handle when an input string is not NULL terminated (CWE-170), leading to buffer over-read (CWE-125) or heap-based buffer overflow (CWE-122).
https://www.cve.org/CVERecord?id=CVE-2009-2523

CVE-2021-29529
Chain: machine-learning product can have a heap-based
buffer overflow (CWE-122) when some integer-oriented bounds are
calculated by using ceiling() and floor() on floating point values
(CWE-1339)
https://www.cve.org/CVERecord?id=CVE-2021-29529

CVE-2010-1866
Chain: integer overflow (CWE-190) causes a negative signed value, which later bypasses a maximum-only check (CWE-839), leading to heap-based buffer overflow (CWE-122).
https://www.cve.org/CVERecord?id=CVE-2010-1866

Memory Management

Memory

Heap overflow

SFP8
Faulty Buffer Access

STR31-C
Guarantee that storage for strings has sufficient space for character data and the null terminator
CWE More Specific

Part 4-2
Req CR 3.5

Part 3-3
Req SR 3.5

Part 4-1
Req SI-1

Part 4-1
Req SI-2

Part 4-1
Req SVV-1

Part 4-1
Req SVV-3

Allowed
This CWE entry is at the Variant 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.

There is significant inconsistency
regarding the "buffer overflow" term, which can have
multiple interpretations and uses. Many people mean
"writing past the end of a buffer." Others mean "writing
past the end of a buffer, or before the beginning of a
buffer." Still others might include "read" in the term.

CLASP
2006-07-19
Draft 3
2006-07-19

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

KDM Analytics
2008-08-01
added/updated white box definitions

CWE Content Team
MITRE
2008-09-08
updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities

CWE Content Team
MITRE
2008-11-24
updated Common_Consequences, Other_Notes, Relationship_Notes

CWE Content Team
MITRE
2009-01-12
updated Common_Consequences, Relationships

CWE Content Team
MITRE
2009-10-29
updated Relationships

CWE Content Team
MITRE
2010-02-16
updated References

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

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

CWE Content Team
MITRE
2012-10-30
updated Demonstrative_Examples

CWE Content Team
MITRE
2013-02-21
updated Demonstrative_Examples, Potential_Mitigations

CWE Content Team
MITRE
2014-06-23
updated Observed_Examples

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

CWE Content Team
MITRE
2017-11-08
updated Causal_Nature, Likelihood_of_Exploit, Observed_Examples, References, Relationships, Taxonomy_Mappings, White_Box_Definitions

CWE Content Team
MITRE
2018-03-27
updated References

CWE Content Team
MITRE
2019-01-03
updated Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated References

CWE Content Team
MITRE
2021-07-20
updated Observed_Examples

CWE Content Team
MITRE
2023-04-27
updated Detection_Factors, Potential_Mitigations, References, Relationships, Time_of_Introduction

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, Taxonomy_Mappings

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

CWE Content Team
MITRE
2025-09-09
4.18
2025-09-09
updated Functional_Areas, References

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Alternate_Terms, Applicable_Platforms, Detection_Factors, Observed_Examples, References, Relationship_Notes, Terminology_Notes

CWE Content Team
MITRE
2026-01-21
4.19.1
2026-01-21
updated Relationships

participants in the CWE ICS/OT SIG 62443 Mapping Fall Workshop
2023-11-14
4.14
2024-02-29
Contributed or reviewed taxonomy mappings for ISA/IEC 62443