# CVE-2025-55640: GPAC MP4Box heap buffer overflow in stbl_AddSize

Source: https://junglewise.ai/threats/cve-2025-55640-a-heap-buffer-overflow-in-the-stbl-addsize-function-isomedia-stbl  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-16. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2025-55640 · Severity: info · Published 2026-10-16

GPAC MP4Box is a command-line tool for encoding and manipulating MP4 media files. A heap buffer overflow flaw in the stbl_AddSize function allows an attacker to crash the application by supplying a crafted MP4 file, resulting in denial of service. Users who process untrusted media files with MP4Box are at risk of application disruption.

Technologies: [Gpac MP4Box](https://junglewise.ai/threats/technologies/mp4box). Vendors: [Gpac](https://junglewise.ai/threats/vendors/gpac).

## Quick answers

**Is CVE-2025-55640 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-55640 being exploited in the wild.

**How severe is CVE-2025-55640?** Informational severity, published 16 October 2026.

**Which products and versions are affected?** Gpac MP4Box v2.4.

**Is there a fix for CVE-2025-55640?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2025-55640 attacked?** It is attacked with local access or over the network, in a software library.

**Am I affected by CVE-2025-55640?** Check whether you run Gpac MP4Box at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A heap buffer overflow exists in the stbl_AddSize function within isomedia/stbl_write.c of GPAC MP4Box v2.4. The vulnerability is triggered when processing a specially crafted MP4 file that causes incorrect size tracking in the sample size box. The attack requires no authentication and is delivered via a malicious file; a local attacker or remote attacker supplying a file can trigger a denial of service condition.

## Affected products

- GPAC MP4Box v2.4

## Timeline

- 2025-10-16: disclosed

## References

- [https://github.com/gpac/gpac/commit/321624f28d19a413449fd1718d1eb59037f8f7fc](https://github.com/gpac/gpac/commit/321624f28d19a413449fd1718d1eb59037f8f7fc)
- [https://github.com/gpac/gpac/issues/3261](https://github.com/gpac/gpac/issues/3261)

## Related threats

- [GPAC MP4Box segmentation fault in dump_isom_saps](https://junglewise.ai/threats/cve-2025-55667-a-segmentation-violation-in-the-dump-isom-saps-function-mp4box)
- [GPAC MP4Box use-after-free in gf_filter_pid_get_packet](https://junglewise.ai/threats/cve-2025-55654-a-use-after-free-in-the-gf-filter-pid-get-packet-function-filter)
- [GPAC MP4Box floating point exception in gf_parse_lfrac](https://junglewise.ai/threats/cve-2025-55653-gpac-mp4box-v2-4-was-discovered-to-contain-a-floating-point)
- [GPAC MP4Box use-after-free in gf_node_deactivate_ex](https://junglewise.ai/threats/cve-2026-90827-gpac-mp4box-use-after-free-in-gf-node-deactivate-ex)
- [GPAC MP4Box out-of-bounds read in gf_node_del](https://junglewise.ai/threats/cve-2026-90826-gpac-mp4box-out-of-bounds-read-in-gf-node-del)