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pypdf Infinite Loop Vulnerability in PDF Merging with Outlines

A vulnerability in pypdf allows an attacker to craft a PDF that causes an infinite loop when merging a file with outlines into a writer.

17 Jun 2026Read 1 minSeverity: schedule it

What changed

A vulnerability in pypdf allows an attacker to craft a PDF that causes an infinite loop when merging a file with outlines into a writer. Fixed in version 6.13.0.

Who it affects

Users of pypdf who merge PDF files with outlines, especially those using versions prior to 6.13.0.

What to do today

Upgrade to pypdf version 6.13.0 or apply the changes from PR #3830 if unable to upgrade.

The trail
Collected Audited Written Published