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pypdf: Unbounded memory usage when parsing PDF without /Length

A vulnerability in pypdf allows an attacker to craft a PDF that leads to large memory usage because MAX_DECLARED_STREAM_LENGTH is sometimes ignored when parsing

19 Jun 2026Read 1 minSeverity: schedule it

What changed

A vulnerability in pypdf allows an attacker to craft a PDF that leads to large memory usage because MAX_DECLARED_STREAM_LENGTH is sometimes ignored when parsing a content stream without a /Length value.

Who it affects

Users of pypdf versions prior to 6.13.3 who parse untrusted PDF files.

What to do today

Upgrade to pypdf==6.13.3 or apply the changes from PR #3871.

The trail
Collected Audited Written Published