CVE-2026-81725

Low

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.

SeverityLow

CVSS3.7

Exploit probability—

ProductNltk

PublishedAug 27, 2026

First seenAug 27, 2026

Weakness typeCWE-400Uncontrolled resource consumption

How to fix

Update

nltk nltk3.10.3 or later
nltk3.10.3 or later

Vendor advisories

github.com/nltk/nltk/security/advisories/GHSA-8mpw-7fpc-4gqj

Affected products

Product	Affected versions	Fixed in
nltk nltk	v < 3.10.3	3.10.3
nltkPyPI	v < 3.10.3	3.10.3

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