---
id: "CVE-2026-125197"
page: "https://infrastack.ai/live/CVE-2026-125197"
kind: "vulnerability"
aliases: ["CVE-2026-125197"]
title: "FFmpeg: crafted AVI or MKV file causes heap out-of-bounds read"
severity: "medium"
cvss: 6.9
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["ffmpeg", "libavcodec", "media-processing", "package"]
not_affected_if: ["trusted-input-only"]
published_at: "2026-11-09T19:16:55+00:00"
first_seen_at: "2026-11-09T19:28:18+00:00"
updated_at: "2026-11-09T19:30:18+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-125197", "first_seen_at": "2026-11-09T19:28:18+00:00"}]
exploit_sources: []
---

# FFmpeg: crafted AVI or MKV file causes heap out-of-bounds read

Link for people: https://infrastack.ai/live/CVE-2026-125197 (this .md is for agents)

FFmpeg's LCL video decoder miscalculates a length when a packet is shorter than 8 bytes, causing a heap out-of-bounds read. An attacker who supplies a crafted AVI or MKV file can crash the decoding application.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed FFmpeg version with `ffmpeg -version`, comparing it against the fixed versions in the product data.
- Look for applications that decode untrusted AVI or MKV files with FFmpeg or libavcodec.

## Timeline

- 2026-11-09T19:28:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-125197

## Documents

- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/ffmpeg-through-9.0.2-heap-out-of-bounds-read-via-lcl-zlib-multithread-decoding
- [fix] Patch: github.com https://github.com/FFmpeg/FFmpeg/commit/12e5d4ec98b7add7bcac9d8131d9a6dfb2549966

## From the sources

FFmpeg through 9.0.2 contains an integer underflow in decode_frame() in libavcodec/lcldec.c that allows attackers to trigger a heap out-of-bounds read via short ZLIB packets with FLAG_MULTITHREAD. Attackers can supply a crafted AVI or MKV file with an LCL video stream whose packet is shorter than 8 bytes, bypassing length clamping to crash the decoding application.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_