CVE-2026-96640

High

Description

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.

SeverityHigh

CVSS7.5

Exploit probability—

Product

Python Pillow

PublishedOct 21, 2026

First seenOct 21, 2026

Weakness typeCWE-400Uncontrolled resource consumption CWE-407CWE-407

How to fix

Update

python pillow13.0.0 or later
pillow13.0.0 or later

Affected products

Product	Affected versions	Fixed in
python pillow	5.1.0 ≤ v < 13.0.0	13.0.0
pillowPyPI	5.1.0 ≤ v < 13.0.0	13.0.0

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