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PYSEC-2026-3015

pypdf possibly has long runtimes for malformed FlateDecode streams

Quick fix

PYSEC-2026-3015 — pypdf: upgrade to the fixed version with the command below.

pip install --upgrade 'pypdf>=6.7.1'

Details

### Impact

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

### Patches

This has been fixed in [pypdf==6.7.1](https://github.com/py-pdf/pypdf/releases/tag/6.7.1).

### Workarounds

If you cannot upgrade yet, consider applying the changes from PR [#3644](https://github.com/py-pdf/pypdf/pull/3644).

Are you affected?

Enter the version of the package you're using.

Affected packages

PyPI/pypdf

Introduced in: 0Fixed in: 6.7.1

Fixpip install --upgrade 'pypdf>=6.7.1'

References

https://github.com/py-pdf/pypdf/security/advisories/GHSA-9mvc-8737-8j8h[WEB]
https://nvd.nist.gov/vuln/detail/CVE-2026-27026[ADVISORY]
https://github.com/py-pdf/pypdf/pull/3644[WEB]
https://github.com/py-pdf/pypdf/commit/7905842d833f899f1d3228af7e7467ad80277016[WEB]
https://github.com/py-pdf/pypdf[PACKAGE]
https://github.com/py-pdf/pypdf/releases/tag/6.7.1[WEB]
https://pypi.org/project/pypdf[PACKAGE]
https://github.com/advisories/GHSA-9mvc-8737-8j8h[ADVISORY]