---
id: "CVE-2026-125233"
page: "https://infrastack.ai/live/CVE-2026-125233"
kind: "vulnerability"
aliases: ["CVE-2026-125233"]
title: "FFmpeg: crafted subtitles overflow heap during DVB subtitle encoding"
severity: "high"
cvss: 8.5
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["ffmpeg", "libavcodec", "media-processing", "package"]
not_affected_if: ["no-dvbsub-encoding", "trusted-input-only"]
published_at: "2026-11-09T19:17:01+00:00"
first_seen_at: "2026-11-09T19:28:20+00:00"
updated_at: "2026-11-09T19:29:29+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-125233", "first_seen_at": "2026-11-09T19:28:20+00:00"}]
exploit_sources: []
---

# FFmpeg: crafted subtitles overflow heap during DVB subtitle encoding

Link for people: https://infrastack.ai/live/CVE-2026-125233 (this .md is for agents)

FFmpeg's DVB subtitle encoder miscounts CLUT segment header size by two bytes, so a crafted file with many bitmap subtitle rectangles writes past its output buffer. An attacker who gets a file transcoded can corrupt heap memory, which may allow code execution.

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

## How to check

- Run `ffmpeg -version` and compare against the fixed release in the product ranges (unknown in the sources).
- Check whether your pipelines transcode DVB subtitles with the dvbsub encoder (unknown in the sources).

## Fix

- Move to a patched FFmpeg build; the fixed version is not stated in the sources. See the linked patch on github.com.

## Timeline

- 2026-11-09T19:28:20+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-125233

## Documents

- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/ffmpeg-through-9.0.2-heap-buffer-overflow-via-dvb-subtitle-encoder
- [fix] Patch: github.com https://github.com/FFmpeg/FFmpeg/commit/7f80b2ad83f37a4998d9617495c92b28a7339a90

## From the sources

FFmpeg through 9.0.2 contains a heap buffer overflow vulnerability in dvbsub_encode() in libavcodec/dvbsubenc.c that undercounts each CLUT segment header by two bytes. Attackers can supply a file with many bitmap subtitle rectangles that, when transcoded to the dvbsub encoder, writes past the output buffer and corrupts heap memory.

---

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