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.
Advisories
Source ID Title
Github GHSA Github GHSA GHSA-4f6g-68pf-7vhv pypdf has possible long runtimes for malformed startxref
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Tue, 13 Jan 2026 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H'}

threat_severity

Moderate


Mon, 12 Jan 2026 17:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Mon, 12 Jan 2026 14:45:00 +0000

Type Values Removed Values Added
First Time appeared Py-pdf
Py-pdf pypdf
Vendors & Products Py-pdf
Py-pdf pypdf

Sat, 10 Jan 2026 05:00:00 +0000

Type Values Removed Values Added
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.
Title pypdf has possible long runtimes for malformed startxref
Weaknesses CWE-1333
CWE-400
References
Metrics cvssV4_0

{'score': 2.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-01-12T16:48:53.503Z

Reserved: 2026-01-08T19:23:09.855Z

Link: CVE-2026-22691

cve-icon Vulnrichment

Updated: 2026-01-12T16:48:50.916Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-01-10T05:16:08.680

Modified: 2026-01-13T14:03:18.990

Link: CVE-2026-22691

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-01-10T04:46:12Z

Links: CVE-2026-22691 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-01-12T14:36:39Z

Weaknesses