CVE-2026-96640

Pillow PDF append accepts malformed shared page-tree DAG causing resource exhaustion

State: Published
Severity: 8.2 High
Published: Oct 21, 2026
Updated: Oct 28, 2026
Reserved: Sep 23, 2026

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.

Scores

CVSS	Score	Vector	Source
4.0	8.2 High	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N	GitHub_M

Weaknesses

CWE-400 Uncontrolled Resource Consumption
CWE-407 Inefficient Algorithmic Complexity

Affected Products

Product	Versions
Pillowpython-pillow	>= 5.1.0, < 13.0.0Affected

References

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