CVE-2026-84309: pypdf: Possible infinite loop for TreeObject.insert_child

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: 2026-09-01 · updated 2026-10-05
Weakness: CWE-835

Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.16.0, an attacker can craft a PDF whose cyclic tree structure causes pypdf/generic/_data_structures.py TreeObject.insert_child to follow /Next links indefinitely when a writing code path inserts a child, producing an infinite loop. This issue is fixed in version 6.16.0.

Affected products

py-pdf pypdf: before 6.16.0 — fixed in 6.16.0

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.16.0. Check the vendor advisory for mitigations.

References

https://github.com/py-pdf/pypdf/commit/c9ba557d565d57c53a0b3a0be06c0a4c29b0559b
https://github.com/py-pdf/pypdf/pull/3964
https://github.com/py-pdf/pypdf/releases/tag/6.16.0
https://github.com/py-pdf/pypdf/security/advisories/GHSA-jp53-mhqp-8xcg

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