---
id: "CVE-2026-120246"
kind: "vulnerability"
aliases: ["CVE-2026-120246"]
title: "FFmpeg: CDXL decoder leaks stack memory into decoded video pixels"
severity: "medium"
cvss: 6.8
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["ffmpeg", "media-processing", "package", "self-hosted"]
not_affected_if: ["cdxl-not-used", "no-untrusted-media"]
published_at: "2026-11-01T01:17:18+00:00"
first_seen_at: "2026-11-01T01:47:22+00:00"
updated_at: "2026-11-01T01:47:38+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-120246", "first_seen_at": "2026-11-01T01:47:22+00:00"}]
---

# FFmpeg: CDXL decoder leaks stack memory into decoded video pixels

FFmpeg's CDXL decoder reads palette entries it never initialized when decoding HAM-encoded frames. A crafted CDXL file can make decoded output contain leftover stack bytes and pointer fragments, which can leak memory contents.

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

## How to check

- Run `ffmpeg -version` and compare against the affected range 4.4 through 9.0.2.
- Check whether FFmpeg is built with the CDXL decoder enabled (`ffmpeg -decoders | grep cdxl`).

## Timeline

- 2026-11-01T01:47:22+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-120246

## From the sources

FFmpeg 4.4 through 9.0.2 contains a use of uninitialized variable vulnerability in the CDXL decoder that leaks stack memory into decoded pixels via unfilled HAM palette entries. Attackers can craft a type-0 CDXL file whose HAM pixels select unfilled new_palette entries in cdxl_decode_ham8() or cdxl_decode_ham6(), exposing stack bytes and pointer fragments in the BGR24 output.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_