CVE-2026-96640 – Pillow PDF append accepts malformed shared page-tree DAG causing resource exhaustion

​CVE ID :CVE-2026-96640

Published : Oct. 21, 2026, 9:20 p.m. | 15 minutes ago

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.

Severity: 8.2 | HIGH

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