HIGH8.7

PYSEC-2026-4156

pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)

Quick fix

PYSEC-2026-4156 — pypdf: upgrade to the fixed version with the command below.

pip install --upgrade 'pypdf>=6.18.1'

Details

### Impact

An attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires a partially malformed `/FlateDecode` stream, where the byte-by-byte decompression is used.

### Patches

This has been fixed in [pypdf==6.18.1](https://github.com/py-pdf/pypdf/releases/tag/6.18.1).

### Workarounds

If you cannot upgrade yet, consider applying the changes from PR [#4073](https://github.com/py-pdf/pypdf/pull/4073).

Are you affected?

Enter the version of the package you're using.

Affected packages

PyPI/pypdf

Introduced in: 0Fixed in: 6.18.1

Fixpip install --upgrade 'pypdf>=6.18.1'

References

https://github.com/py-pdf/pypdf/security/advisories/GHSA-jw7q-gvrg-4vj3[WEB]
https://nvd.nist.gov/vuln/detail/CVE-2026-102997[ADVISORY]
https://github.com/py-pdf/pypdf/pull/4073[WEB]
https://github.com/py-pdf/pypdf/commit/d9d38cf99b115deb562d3b68f36c33027bc04f79[WEB]
https://github.com/py-pdf/pypdf[PACKAGE]
https://github.com/py-pdf/pypdf/releases/tag/6.18.1[WEB]
https://pypi.org/project/pypdf[PACKAGE]
https://github.com/advisories/GHSA-jw7q-gvrg-4vj3[ADVISORY]