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().

What CVEs are caused by CWE-122?

2,270 recorded CVEs are attributed to CWE-122, including CVE-2024-38812, CVE-2025-21333, CVE-2023-27997. 17 are listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.

How is CWE-122 detected?

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.

What are the consequences of CWE-122?

Exploiting CWE-122 can lead to: DoS: Crash, Exit, or Restart, DoS: Resource Consumption (CPU), DoS: Resource Consumption (Memory), Execute Unauthorized Code or Commands, Bypass Protection Mechanism, Modify Memory.

Is CWE-122 actively exploited?

Yes. 17 CWE-122 vulnerabilities are in CISA's KEV catalog of actively exploited flaws, out of 2,270 recorded CVEs.

CWE-122: Heap-based Buffer Overflow (Heap Overflow)

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How to prevent it

Practical mitigations for CWE-122, grouped by where in the lifecycle they apply.

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.

Effectiveness: Defense in Depth

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].

Effectiveness: 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.

Code examples

Illustrative examples from MITRE showing how the weakness appears in code.

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

Vulnerable example

#define BUFSIZE 256

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.

Vulnerable example

char * copy_input(char *user_supplied_string){

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.

CWE-122: Heap-based Buffer Overflow

Overview

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Fuzzing

Automated Dynamic Analysis

Code examples

Illustrative examples

Terminology & mappings

Alternate terms

Mapped taxonomies

Attack patterns

Frequently asked questions

References

Stay ahead of CWE-122

Overview

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Fuzzing

Automated Dynamic Analysis

Code examples

Illustrative examples

Related weaknesses

Parent

Terminology & mappings

Alternate terms

Mapped taxonomies

Attack patterns

Frequently asked questions

References

Stay ahead of CWE-122