CVE-2026-48156: pypdf: Possible long runtimes for zero-only width values in cross-reference streams

Severity: low (CVSS 3.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-28 · updated 2026-10-14
Weakness: CWE-834

Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.12.0, an attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires cross-reference streams with /W [0 0 0] values and large /Size values. This vulnerability is fixed in 6.12.0.

Affected products

py-pdf pypdf: before 6.12.0 — fixed in 6.12.0

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.12.0. Check the vendor advisory for mitigations.

References

https://github.com/py-pdf/pypdf/pull/3791
https://github.com/py-pdf/pypdf/releases/tag/6.12.0
https://github.com/py-pdf/pypdf/security/advisories/GHSA-248m-82v9-q6g6

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