What’s Vulnerable › Vulnerabilities

CVE-2026-22691: pypdf has possible long runtimes for malformed startxref

• Severity: medium (CVSS 5.3 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: 2026-01-10 · updated 2026-06-17
• Weakness: CWE-400

Description

pypdf is a free and open-source pure-python PDF library. Prior to version 6.6.0, pypdf has possible long runtimes for malformed startxref. An attacker who uses this vulnerability can craft a PDF which leads to possibly long runtimes for invalid startxref entries. When rebuilding the cross-reference table, PDF files with lots of whitespace characters become problematic. Only the non-strict reading mode is affected. Only the non-strict reading mode is affected. This issue has been patched in version 6.6.0.

Affected products

• py-pdf pypdf: before 6.6.0 — fixed in 6.6.0

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.6.0. Check the vendor advisory for mitigations.

References

• https://github.com/py-pdf/pypdf/commit/294165726b646bb7799be1cc787f593f2fdbcf45
• https://github.com/py-pdf/pypdf/pull/3594
• https://github.com/py-pdf/pypdf/releases/tag/6.6.0
• https://github.com/py-pdf/pypdf/security/advisories/GHSA-4f6g-68pf-7vhv

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