CVE-2023-46929 is a high severity flaw in GPAC's MP4Box tool, scored 7.5, where a malformed input crashes the application inside gf_avc_change_vui. The GPAC maintainers closed the report with a null guard commit on 26 October 2023. Rebuild or update to a GPAC that includes that commit, and avoid feeding untrusted media to older builds.
What's affected
The NVD record names GPAC 2.3-DEV-rev605-gfc9e29089-master, the development build the reporter tested, and points at the function gf_avc_change_vui in src/media_tools/av_parsers.c. The impact is a crash of MP4Box, which the record describes as allowing attackers to crash the application.
The fix is upstream commit 4248def, titled "add nullguard on gf_avc_change_vui (fixes #2662)". The GitHub issue was closed by that commit. I could not confirm which numbered GPAC release first shipped it, so check your distribution's changelog or the GPAC release notes rather than assuming a version number.
The record scores the flaw as network reachable with no privileges, which is how NVD often scores a command line parser. In practice you are exposed where a service runs MP4Box or the GPAC libraries on files that users or partners upload.
The NVD record was published on 2024-01-03, scores 7.5 (High), and carries the vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Weakness class: CWE-20.
How to check if you're exposed
Start with the version of the tool you run, then see whether your source tree contains the fix.
MP4Box -version
dpkg -l | grep -i gpac
brew list --versions gpac
If you build GPAC from a git checkout, this prints a success message only when the fix commit is already in your history:
git merge-base --is-ancestor 4248def5d24325aeb0e35cacde3d56c9411816a6 HEAD && echo "fix present"
Also search your build pipelines and containers for anything that calls MP4Box on uploaded video. Those are the places where a crash turns into an outage.
What to do now
- Inventory every host, container image and CI job that installs GPAC or MP4Box.
- Update to a build that includes commit 4248def, or rebuild from upstream source that does.
- If a service runs MP4Box on user uploads, run it in a sandbox with a time limit and automatic restart so one bad file cannot stall a queue.
- Reject files that fail basic validation before they reach the parser.
- Re-scan after updating to confirm the old build is gone from images and lockfiles.
Why it matters
The cause is a missing check on a value that can be empty while MP4Box adjusts video usability information for an AVC stream. The upstream fix adds a null guard. The record files the weakness as CWE-20, improper input validation, which is the general class for media parsers that trust the structure of a file.
The effect described is a crash, so the risk is availability rather than data theft. That still matters for transcoding queues and upload pipelines, where one malformed file can repeat failures. The record's KEV flag is false, so this CVE is not on the CISA Known Exploited Vulnerabilities list. The advisory pages I read describe a crash only and do not claim exploitation.
Quick check
Does this let an attacker run code?
The record and the upstream issue describe a crash of MP4Box. Neither claims code execution, so treat it as an availability problem and patch on that basis.
Sources
Last reviewed: 19 October 2026.
