CVE-2026-27628: pypdf has a possible infinite loop when loading circular /Prev entries in cross-reference streams

Severity: high (CVSS 7.5 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: 2026-02-25 · updated 2026-06-17
Weakness: CWE-835

Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.7.2, an attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This requires reading the file. This has been fixed in pypdf 6.7.2. As a workaround, one may apply the patch manually.

Affected products

py-pdf pypdf: before 6.7.2 — fixed in 6.7.2

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.7.2. Check the vendor advisory for mitigations.

References

https://github.com/py-pdf/pypdf/commit/f0a462d36971cf077d74492a348d0d06fd60ea4d
https://github.com/py-pdf/pypdf/issues/3654
https://github.com/py-pdf/pypdf/security/advisories/GHSA-2rw7-x74f-jg35
https://github.com/py-pdf/pypdf/issues/3654

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