CVE-2026-125103 FFmpeg through 9.0.2 Uninitialized Heap Disclosure via MLZ Decompressor in ALS Decoder
Medium 4.8
Published
Updated
Check this codebase for CVE-2026-125103 and fix it if it is affected.
What it is: CVE-2026-125103 is a medium-severity vulnerability in FFmpeg, published on 9 Nov 2026.
Exploitation: There is no known exploitation of CVE-2026-125103 in the wild and no public exploit code.
Affected product: FFmpeg. No package-level version data is available, so check the vendor advisory linked from the reference page.
Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.
Reference: https://insights.sbomify.com/CVE-2026-125103/ (Markdown: https://insights.sbomify.com/CVE-2026-125103/index.md)
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-125103?
CVE-2026-125103 is a medium-severity vulnerability in FFmpeg, published on 9 Nov 2026.
Official description
FFmpeg through 9.0.2 contains an information disclosure vulnerability in ff_mlz_decompression() in libavcodec/mlz.c, which accepts string codes beyond the dictionary's next free code. Attackers can supply a crafted MPEG-4 ALS file with malformed initial or out-of-range codes to copy uninitialized heap bytes into decoded audio output.
Weakness: CWE-908
Which versions are affected by CVE-2026-125103?
How do I fix CVE-2026-125103?
No fix has been published for CVE-2026-125103 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-125103 being exploited?
There is no known exploitation of CVE-2026-125103 in the wild and no public exploit code.
Sources
Also known as GHSA-qw4p-vq2p-9gqc, UBUNTU-CVE-2026-125103.