# CVE-2026-125259: FFmpeg integer overflow in prores_kostya encoder

Source: https://junglewise.ai/threats/cve-2026-125259-ffmpeg-through-9-0-2-contains-an-integer-overflow-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-2026-125259 · Severity: high · CVSS 7.8 · Published 2026-11-09

FFmpeg is a multimedia library used to encode, decode, and process audio and video files. An integer overflow flaw in the ProRes encoder can allow attackers to supply a specially crafted high-resolution video file that causes memory corruption, potentially leading to application crashes or arbitrary code execution during video transcoding.

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

## Quick answers

**Is CVE-2026-125259 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-125259 being exploited in the wild.

**How severe is CVE-2026-125259?** High severity, with a CVSS score of 7.8, published 9 November 2026.

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

**Is there a fix for CVE-2026-125259?** 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-2026-125259 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-125259?** 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 ff_prores_kostya_encode_init() function in FFmpeg uses 32-bit arithmetic to calculate frame_size_upper_bound, causing an integer overflow when processing large frame dimensions. This leads to an undersized packet buffer allocation; when encode_frame() subsequently writes slices to this buffer, it overflows and corrupts heap memory. The vulnerability requires attacker-controlled video input and affects video transcoding workflows using the prores_ks encoder.

## Affected products

- FFmpeg FFmpeg through 9.0.2

## Timeline

- 2026-11-09: disclosed
- 2026-10-30: patched: Fix merged to master branch prior to public disclosure

## 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)

## Related threats

- [FFmpeg heap out-of-bounds read in v4l2_buffers](https://junglewise.ai/threats/cve-2026-125270-ffmpeg-through-9-0-2-contains-a-heap-out-of-bounds-read)
- [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)