CVE-2026-33123: pypdf has inefficient decoding of array-based streams

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-20 · updated 2026-06-17
Weakness: CWE-400

Description

pypdf is a free and open-source pure-python PDF library. Versions prior to 6.9.1 allow an attacker to craft a malicious PDF which leads to long runtimes and/or large memory usage. Exploitation requires accessing an array-based stream with many entries. This issue has been fixed in version 6.9.1.

Affected products

py-pdf pypdf: before 6.9.1 — fixed in 6.9.1

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.9.1. Check the vendor advisory for mitigations.

References

https://github.com/py-pdf/pypdf/pull/3686
https://github.com/py-pdf/pypdf/releases/tag/6.9.1
https://github.com/py-pdf/pypdf/security/advisories/GHSA-qpxp-75px-xjcp

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