# CVE-2026-125256: FFmpeg heap buffer overflow in Huffyuv encoder

Source: https://junglewise.ai/threats/cve-2026-125256-ffmpeg-through-9-0-2-contains-a-heap-buffer-overflow  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-09. Updated: 2026-11-09  
License: CC BY 4.0 with a link back

CVE-2026-125256 · Severity: high · CVSS 7 · Published 2026-11-09

FFmpeg is a widely-used multimedia framework that encodes and transcodes video. A heap buffer overflow in the Huffyuv video encoder can corrupt memory and crash the application when processing maliciously crafted or abnormally-sized video files. Attackers can exploit this by supplying video narrower than 8 or 16 pixels to trigger out-of-bounds writes on RISC-V systems with RVV extensions enabled.

Technologies: [Ffmpeg](https://junglewise.ai/threats/technologies/ffmpeg). Vendors: [Ffmpeg](https://junglewise.ai/threats/vendors/ffmpeg).

## Quick answers

**Is CVE-2026-125256 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-125256 being exploited in the wild.

**How severe is CVE-2026-125256?** High severity, with a CVSS score of 7, published 9 November 2026.

**Which products and versions are affected?** Ffmpeg through 9.0.2.

**Is there a fix for CVE-2026-125256?** Yes: fixed in FFmpeg 9.1. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-125256 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-125256?** Check whether you run Ffmpeg at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in FFmpeg 9.1

## Technical details

The vulnerability exists in the ff_llvidenc_diff_bytes_rvv() function in the RISC-V/RVV implementation of the Huffyuv encoder. Negative length values passed to this function cause heap buffer overflows when the encoder processes RGB video frames narrower than 8 or 16 pixels. The flaw is specific to RVV-enabled RISC-V builds and allows writes past the encoder's temporary buffer.

## Affected products

- FFmpeg FFmpeg through 9.0.2

## Timeline

- 2026-11-09: disclosed
- 2026-10-30: patched: Fix merged in PR #25573

## References

- [https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/25573](https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/25573)
- [https://github.com/FFmpeg/FFmpeg](https://github.com/FFmpeg/FFmpeg)

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