# CVE-2026-81725: nltk: NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows at...

CVE-2026-81725 is fixed in nltk on 1 platform by DEBIAN-CVE-2026-81725 (version 3.10.3-1), released August 28, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-81725
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0037
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 27, 2026

## Description

NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the read_block method through public APIs like words() and tagged_words() to force repeated rescans and achieve near-quadratic runtime growth.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | nltk Debian 14 | 3.10.3-1 | [DEBIAN-CVE-2026-81725](https://patchblox.com/security/data/fix/linux/debian-cve-2026-81725.md) | Aug 28, 2026 |

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Data as of 2026-11-09T19:38:12Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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