---
id: CVE-2026-125103
title: >-
  FFmpeg through 9.0.2 Uninitialized Heap Disclosure via MLZ Decompressor in ALS
  Decoder
summary: >-
  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 m…
severity: low
cvss: 3.3
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N'
cvssSource: cna
cwe:
  - CWE-908
vendor: FFmpeg
product: FFmpeg
affected:
  - FFmpeg <= 9.0.2
published: '2026-11-09'
updated: '2026-11-09'
sourceUpdated: '2026-11-09T19:10:57.722Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-125103'
references:
  - url: 'https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/25703'
  - url: >-
      https://github.com/FFmpeg/FFmpeg/commit/db98784a72600a94f7ebd5f016a37e01a505c27b
    label: Patch Commit
  - url: 'https://github.com/FFmpeg/FFmpeg/blob/n9.0.2/libavcodec/mlz.c#L161'
  - url: 'https://github.com/FFmpeg/FFmpeg'
  - url: >-
      https://www.vulncheck.com/advisories/ffmpeg-through-9.0.2-uninitialized-heap-disclosure-via-mlz-decompressor-in-als-decoder
    label: >-
      VulnCheck Advisory: FFmpeg through 9.0.2 Uninitialized Heap Disclosure via
      MLZ Decompressor in ALS Decoder
tags:
  - cve.org
ingestedAt: '2026-11-09T19:18:02.628Z'
---

## Overview

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.

## Affected

- `FFmpeg <= 9.0.2`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.