# CVE-2026-125246: FFmpeg denial of service in JPEG bitstream parsing

Source: https://junglewise.ai/threats/cve-2026-125246-ffmpeg-through-9-0-2-contains-a-denial-of-service-vulnerability  
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-2026-125246 · Severity: medium · CVSS 4.7 · Published 2026-11-09

FFmpeg is a widely-used multimedia processing library that decodes and processes audio and video files. A malicious JPEG or MJPEG stream can cause FFmpeg to crash due to incorrect handling of byte-stuffing markers in scan headers, disrupting video playback and processing services that rely on FFmpeg.

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

## Quick answers

**Is CVE-2026-125246 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-125246 being exploited in the wild.

**How severe is CVE-2026-125246?** Medium severity, with a CVSS score of 4.7, published 9 November 2026.

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

**Is there a fix for CVE-2026-125246?** Yes: fixed in FFmpeg 9.1 and later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-125246 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-125246?** 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 and later

## Technical details

The cbs_jpeg_assemble_fragment() function miscounts 0xff stuffing bytes in JPEG scan headers, causing CBS-based bitstream filters to miscalculate buffer sizes. Attackers supply a crafted JPEG/MJPEG stream with 0xff bytes in the scan header, triggering an av_assert0 abort when the bitstream is parsed. The fix counts byte-stuffing only in the entropy-coded portion of the scan data, not the header itself.

## Affected products

- FFmpeg FFmpeg through 9.0.2

## Timeline

- 2026-11-09: disclosed
- 2026-10-25: patched

## References

- [https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/25232](https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/25232)
- [https://github.com/FFmpeg/FFmpeg](https://github.com/FFmpeg/FFmpeg)

## Related threats

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- [FFmpeg double free in H.264 SEI message handling](https://junglewise.ai/threats/cve-2026-125269-ffmpeg-through-9-0-2-contains-a-double-free-vulnerability-in)
- [FFmpeg heap out-of-bounds write in APAC decoder](https://junglewise.ai/threats/cve-2026-125267-ffmpeg-before-8-1-3-and-9-x-before-9-0-2-contains-a-heap-out-of)
- [FFmpeg use-after-free in NVIDIA codec decoding](https://junglewise.ai/threats/cve-2026-125265-ffmpeg-through-9-0-2-contains-a-use-after-free-vulnerability-in)
- [FFmpeg JPEG XL parser uncontrolled resource consumption](https://junglewise.ai/threats/cve-2026-125264-ffmpeg-through-9-0-2-contains-an-uncontrolled-resource)