CWE-680 Compound Draft

Integer Overflow to Buffer Overflow

This vulnerability occurs when a program calculates the size of memory to allocate, but an integer overflow in that calculation results in a much smaller buffer being created than intended. This…

Definition

What is CWE-680?

This vulnerability occurs when a program calculates the size of memory to allocate, but an integer overflow in that calculation results in a much smaller buffer being created than intended. This undersized buffer can then be overflowed by subsequent operations, corrupting adjacent memory.
At its core, this is a two-stage flaw. First, during a size calculation—like multiplying length by element size—an integer overflow wraps the result to a deceptively small number. The program then allocates a buffer based on this incorrect size, believing it's sufficient. The real danger follows when the application, operating on the original, larger data size, writes more data into this tiny buffer than it can hold, leading to a classic buffer overflow. Developers can prevent this by using strict input validation on all size calculations and employing safe integer operations or libraries that check for overflow before allocation. Always assume that arithmetic involving user-influenced values can overflow, and design memory allocation logic to fail safely rather than proceeding with a corrupted size.
Real-world impact

Real-world CVEs caused by CWE-680

  • 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)

  • CVE-2017-1000121

    chain: unchecked message size metadata allows integer overflow (CWE-190) leading to buffer overflow (CWE-119).

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable C

The following image processing code allocates a table for images.

Vulnerable C 
img_t table_ptr; /*struct containing img data, 10kB each*/
  int num_imgs;
  ...
  num_imgs = get_num_imgs();
  table_ptr = (img_t*)malloc(sizeof(img_t)*num_imgs);
  ...
Secure code example

Secure pseudo

Secure pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-680

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Detection signals

How to detect CWE-680

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-680 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-680?

This vulnerability occurs when a program calculates the size of memory to allocate, but an integer overflow in that calculation results in a much smaller buffer being created than intended. This undersized buffer can then be overflowed by subsequent operations, corrupting adjacent memory.

How serious is CWE-680?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-680?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-680?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

How does Plexicus detect and fix CWE-680?

Plexicus's SAST engine matches the data-flow signature for CWE-680 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-680?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/680.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-680

CWE-190 Parent

Integer Overflow or Wraparound

Integer overflow or wraparound occurs when a calculation produces a numeric result that exceeds the maximum value a variable can hold.…

Resources

Further reading

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