CVE-2026-54651: pypdf: Possible infinite loop when processing threads/articles in writer

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-22 · updated 2026-10-25
Weakness: CWE-835

Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.13.1, an attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This requires merging a file with threads/articles into a writer. This vulnerability is fixed in 6.13.1.

Affected products

py-pdf pypdf: before 6.13.1 — fixed in 6.13.1

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.13.1. Check the vendor advisory for mitigations.

References

https://github.com/py-pdf/pypdf/pull/3839
https://github.com/py-pdf/pypdf/releases/tag/6.13.1
https://github.com/py-pdf/pypdf/security/advisories/GHSA-g9xf-7f8q-9mcj

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