CVE-2026-27888: pypdf: Manipulated FlateDecode XFA streams can exhaust RAM

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: 2026-02-26 · updated 2026-06-17
Weakness: CWE-400

Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.7.3, an attacker who uses this vulnerability can craft a PDF which leads to the RAM being exhausted. This requires accessing the `xfa` property of a reader or writer and the corresponding stream being compressed using `/FlateDecode`. This has been fixed in pypdf 6.7.3. As a workaround, apply the patch manually.

Affected products

py-pdf pypdf: before 6.7.3 — fixed in 6.7.3

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.7.3. Check the vendor advisory for mitigations.

References

https://github.com/py-pdf/pypdf/commit/7a4c8246ed48d9d328fb596942271da47b6d109c
https://github.com/py-pdf/pypdf/pull/3658
https://github.com/py-pdf/pypdf/releases/tag/6.7.3
https://github.com/py-pdf/pypdf/security/advisories/GHSA-x7hp-r3qg-r3cj

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