CVE-2026-27026

pypdf possibly has long runtimes for malformed FlateDecode streams

State: Published
Severity: 6.9 Medium
Published: Feb 20, 2026
Updated: Feb 24, 2026
Reserved: Feb 17, 2026

Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.7.1, an attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires a malformed /FlateDecode stream, where the byte-by-byte decompression is used. This vulnerability is fixed in 6.7.1.

Scores

CVSS	Score	Vector	Source
4.0	6.9 Medium	CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N	GitHub_M

Weaknesses

CWE-770 Allocation of Resources Without Limits or Throttling

Affected Products

Product	Versions
pypdfpy-pdf	< 6.7.1Affected

References

https://github.com/py-pdf/pypdf/security/advisories/GHSA-9mvc-8737-8j8h
https://github.com/py-pdf/pypdf/pull/3644
https://github.com/py-pdf/pypdf/commit/7905842d833f899f1d3228af7e7467ad80277016
https://github.com/py-pdf/pypdf/releases/tag/6.7.1

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