# CVE-2026-96639: Pillow out-of-bounds write in multi-frame image loaders

Source: https://junglewise.ai/threats/cve-2026-96639-pillow-is-a-python-imaging-library-from-11-0-0-until-13-0-0-multi  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-21. Updated: 2026-10-21  
License: CC BY 4.0 with a link back

CVE-2026-96639 · Severity: critical · CVSS 9.8 · Published 2026-10-21

Pillow is a Python library for image processing and manipulation. Versions 11.0.0 through 12.x contain a flaw where multi-frame image files (PSD, MPO, DCX, or MIC formats) can trigger buffer overflows when frame transitions change the image mode or dimensions. Attackers can craft malicious files to cause crashes or potentially execute arbitrary code by writing data outside allocated memory boundaries.

Technologies: [pillow (PyPI)](https://junglewise.ai/threats/technologies/pillow), [Python Pillow Pillow](https://junglewise.ai/threats/technologies/python-pillow-pillow). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi), [Python Pillow](https://junglewise.ai/threats/vendors/python-pillow).

## Quick answers

**Is CVE-2026-96639 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-96639 being exploited in the wild.

**How severe is CVE-2026-96639?** Critical severity, with a CVSS score of 9.8, published 21 October 2026.

**Which products and versions are affected?** pillow (PyPI) >= 11.0.0, < 13.0.0, ECOSYSTEM:introduced=11.0.0,fixed=13.0.0; Python Pillow Pillow 11.0.0 to 12.x.

**Is there a fix for CVE-2026-96639?** Yes. pillow (PyPI): upgrade to 13.0.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-96639 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-96639?** Check whether you run pillow (PyPI) or Python Pillow Pillow 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

- pillow (PyPI): upgrade to 13.0.0 or later

  ```sh
  pip install "pillow>=13.0.0"
  ```


## Technical details

The vulnerability exists in ImageFile.load_prepare(), which reuses a stale ImagingCore allocation without verifying that the frame's mode and size match the previously allocated buffer. When a multi-frame file transitions to a frame with wider color data (RGB or CMYK from a narrower mode) while keeping the same dimensions, the decoder writes wider pixels into the undersized allocation, causing out-of-bounds writes. The MPO format path can also trigger native over-reads, leading to potential code execution in certain runtime contexts.

## Affected products

- Python Pillow Pillow 11.0.0 to 12.x

## Identifiers

- CVE-2026-96639
- BIT-PILLOW-2026-96639
- GHSA-v9pv-5gc8-w2m6
- PYSEC-2026-4339

## Timeline

- 2026-10-21: disclosed
- 2026-10-03: patched: Fix committed but released in version 13.0.0

## References

- [https://github.com/python-pillow/Pillow/commit/78d97d994579aef81aafe123773d525f40f2522a](https://github.com/python-pillow/Pillow/commit/78d97d994579aef81aafe123773d525f40f2522a)
- [https://github.com/python-pillow/Pillow/pull/10105](https://github.com/python-pillow/Pillow/pull/10105)

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