---
id: CVE-2026-96640
title: >-
  Pillow PDF append accepts malformed shared page-tree DAG causing resource
  exhaustion
summary: >-
  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", a…
severity: high
cvss: 8.2
cvssVector: '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'
cvssSource: cna
cwe:
  - CWE-400
  - CWE-407
vendor: python-pillow
product: Pillow
affected:
  - 'Pillow >= 5.1.0, < 13.0.0'
published: '2026-10-21'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T21:03:22.785Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-96640'
references:
  - url: >-
      https://github.com/python-pillow/Pillow/security/advisories/GHSA-mrfp-p49p-3hf2
    label: >-
      https://github.com/python-pillow/Pillow/security/advisories/GHSA-mrfp-p49p-3hf2
  - url: 'https://github.com/python-pillow/Pillow/pull/10093'
    label: 'https://github.com/python-pillow/Pillow/pull/10093'
  - url: >-
      https://github.com/python-pillow/Pillow/commit/6f0e7ee1f9c2fe227906f8a4b926e6622b702bc7
    label: >-
      https://github.com/python-pillow/Pillow/commit/6f0e7ee1f9c2fe227906f8a4b926e6622b702bc7
  - url: 'https://github.com/python-pillow/Pillow/releases/tag/13.0.0'
    label: 'https://github.com/python-pillow/Pillow/releases/tag/13.0.0'
tags:
  - cve.org
ingestedAt: '2026-10-21T22:18:33.775Z'
---

## Overview

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.

## Affected

- `Pillow >= 5.1.0, < 13.0.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.