CVE-2026-96640

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

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

Weaknesses (CWE)

• CWE-400
• CWE-407

Advisories

• GHSA-mrfp-p49p-3hf2 — Pillow PDF append accepts malformed shared page-tree DAG causing resource exhaustion

European references

• ENISA EUVD · EUVD-2026-107570
• GCVE · GCVE-0-2026-96640

Affected configurations (NVD CPE)

• cpe:2.3:a:python:pillow:*:*:*:*:*:*:*:* ≥ 5.1.0 < 13.0.0

Affected products

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

Sources