CVE-2026-96640

Pillow is a Python imaging library. From 5.1.0 until 13.0.0, PdfParser.linearize_page_tree() in src/PIL/PdfParser.py treats a PDF /Pages graph as a tree without tracking duplicate indirect references. When Image.save(..., format="PDF", append=True) processes an attacker-controlled existing PDF whose /Kids arrays repeatedly reference the same child /Pages node, Pillow expands the shared subtree as distinct pages. A compact malformed PDF can therefore create exponentially many page references and consume disproportionate CPU before the append completes. This issue is fixed in version 13.0.0.

Score

CVSS 4.0 8.2 High

Status

Modified - security-advisories@github.com

Published

2026-10-21

Last modified

2026-10-28

Weaknesses

CWE-400, CWE-407

Affected products

• Pillow (Python)
• Pillow (Python-pillow)

References

• https://github.com/python-pillow/Pillow/security/advisories/GHSA-mrfp-p49p-3hf2
• https://github.com/python-pillow/Pillow/pull/10093
• https://github.com/python-pillow/Pillow/commit/6f0e7ee1f9c2fe227906f8a4b926e6622b702bc7
• https://github.com/python-pillow/Pillow/releases/tag/13.0.0