CVE-2026-28804: pypdf: Inefficient decoding of ASCIIHexDecode streams

Severity: medium (CVSS 5.3 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: 2026-03-06 · updated 2026-06-17
Weakness: CWE-407

Description

pypdf is a free and open-source pure-python PDF library. Prior to version 6.7.5, an attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires accessing a stream which uses the /ASCIIHexDecode filter. This issue has been patched in version 6.7.5.

Affected products

py-pdf pypdf: before 6.7.5 — fixed in 6.7.5

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.7.5. Check the vendor advisory for mitigations.

References

https://github.com/py-pdf/pypdf/commit/648c627d2657447dfb1773412af05a0a5103b98f
https://github.com/py-pdf/pypdf/pull/3666
https://github.com/py-pdf/pypdf/releases/tag/6.7.5
https://github.com/py-pdf/pypdf/security/advisories/GHSA-9m86-7pmv-2852

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