---
id: "CVE-2026-125221"
page: "https://infrastack.ai/live/CVE-2026-125221"
kind: "vulnerability"
aliases: ["CVE-2026-125221"]
title: "FFmpeg: crafted FLAC input exhausts stack and crashes the process"
severity: "medium"
cvss: 6.8
epss: null
exploited: false
status: "open"
category: "runtime"
products: [{"name": "FFmpeg", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["ffmpeg", "media-processing", "runtime", "self-hosted"]
not_affected_if: ["no-untrusted-flac-input", "trusted-files-only"]
published_at: "2026-11-09T19:16:59+00:00"
first_seen_at: "2026-11-09T19:28:19+00:00"
updated_at: "2026-11-09T19:31:26+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-125221", "first_seen_at": "2026-11-09T19:28:19+00:00"}]
exploit_sources: []
---

# FFmpeg: crafted FLAC input exhausts stack and crashes the process

Link for people: https://infrastack.ai/live/CVE-2026-125221 (this .md is for agents)

FFmpeg through 9.0.2 recurses without limit in score_header() in the FLAC parser, so a crafted FLAC file exhausts the thread stack. An attacker who gets a program to demux the file can crash that process.

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

## Affected

- vendor:FFmpeg affected range not listed fixed no fixed version listed

## How to check

- Run `ffmpeg -version` and compare against the fixed version in the patch linked from NVD.
- Check whether any service accepts untrusted FLAC uploads and passes them to FFmpeg for demuxing or probing.

## Fix

- FFmpeg: unknown (the sources name a patch on github.com but do not state the fixed version)

## Timeline

- 2026-11-09T19:28:19+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-125221

## Documents

- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/ffmpeg-through-9.0.2-uncontrolled-recursion-in-flac-parser-score-header
- [fix] Patch: github.com https://github.com/FFmpeg/FFmpeg/commit/972fe1ccd326538fe9a6b5d5094b7880b5443429

## From the sources

FFmpeg through 9.0.2 contains an uncontrolled recursion vulnerability in score_header() in libavcodec/flac_parser.c that allows attackers to exhaust the thread stack via crafted FLAC input. Attackers can supply a FLAC stream packed with many small valid-looking frame headers, forcing deep recursion that crashes the process during demuxing or parsing.

---

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