What is CVE-2026-125103?

CVE-2026-125103 is a low-severity vulnerability in Ffmpeg, classified under Use of Uninitialized Resource. CVSS score: 3.3/10. Published 2026-11-09.

How severe is CVE-2026-125103?

Low severity. CVSS v3 base score is 3.3 out of 10.

Vulnerability in Ffmpeg

CVE-2026-125103

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.

Published 2026-11-09.

CVSS v3 metric

CVSS v3 base score 3.3 (Low). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Ffmpeg

Weakness classification (CWE)

CWE-908 — Use of Uninitialized Resource

References

code.ffmpeg.org/FFmpeg/FFmpeg/pulls/25703 (issue-tracking)
github.com/FFmpeg/FFmpeg (product)
github.com/FFmpeg/FFmpeg/blob/n9.0.2/libavcodec/mlz.c (technical-description)
github.com/FFmpeg/FFmpeg/commit/db98784a72600a94f7ebd5f016a37e01a505c27b (patch)
www.vulncheck.com/advisories/ffmpeg-through-9.0.2-uninitialized-heap-disclosure… (third-party-advisory)

Frequently asked questions

What is CVE-2026-125103?: CVE-2026-125103 is a low-severity vulnerability in Ffmpeg, classified under Use of Uninitialized Resource. CVSS score: 3.3/10. Published 2026-11-09.
How severe is CVE-2026-125103?: Low severity. CVSS v3 base score is 3.3 out of 10.