CVE-2026-28351: Manipulated RunLengthDecode streams can exhaust RAM

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-02-27 · updated 2026-06-17
Weakness: CWE-400

Description

pypdf is a free and open-source pure-python PDF library. Prior to version 6.7.4, an attacker who uses this vulnerability can craft a PDF which leads to large memory usage. This requires parsing the content stream using the RunLengthDecode filter. This has been fixed in pypdf 6.7.4. As a workaround, consider applying the changes from PR #3664.

Affected products

py-pdf pypdf: before 6.7.4 — fixed in 6.7.4

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.7.4. Check the vendor advisory for mitigations.

References

https://github.com/py-pdf/pypdf/commit/f309c6003746414dc7b5048c19e6d879ff2dc858
https://github.com/py-pdf/pypdf/pull/3664
https://github.com/py-pdf/pypdf/releases/tag/6.7.4
https://github.com/py-pdf/pypdf/security/advisories/GHSA-f2v5-7jq9-h8cg

Get alerted when CVE-2026-28351 or the next vulnerability affects your stack