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PYSEC-2026-3655

pypdf: Possible large memory usage for large /ToUnicode streams

Quick fix

PYSEC-2026-3655 — pypdf: upgrade to the fixed version with the command below.

pip install --upgrade 'pypdf>=6.15.0'

Details

### Impact

An attacker who uses this vulnerability can craft a PDF which leads to large memory consumption. This requires parsing the `/ToUnicode` entry of a font with unusually large values, for example during text extraction.

### Patches

This has been fixed in [pypdf==6.15.0](https://github.com/py-pdf/pypdf/releases/tag/6.15.0).

### Workarounds

If you cannot upgrade yet, consider applying the changes from PR [#3944](https://github.com/py-pdf/pypdf/pull/3944).

Are you affected?

Enter the version of the package you're using.

Affected packages

PyPI / pypdf

Introduced in: 0 Fixed in: 6.15.0

Fix pip install --upgrade 'pypdf>=6.15.0'

References

https://github.com/py-pdf/pypdf/security/advisories/GHSA-fp3f-mc75-235c [WEB]
https://github.com/py-pdf/pypdf/pull/3944 [WEB]
https://github.com/py-pdf/pypdf/commit/afba8080e19d29a3c256a742b340995e695b35aa [WEB]
https://github.com/py-pdf/pypdf [PACKAGE]
https://github.com/py-pdf/pypdf/releases/tag/6.15.0 [WEB]
https://pypi.org/project/pypdf [PACKAGE]
https://github.com/advisories/GHSA-fp3f-mc75-235c [ADVISORY]
https://nvd.nist.gov/vuln/detail/CVE-2026-71870 [ADVISORY]