NLTK Vulnerable to REDoS

HIGH 7.5CVE-2021-3842 · GHSA-rqjh-jp2r-59cj · PYSEC-2022-5 · Published 04/01/2022 · updated 17/06/2026

In short

CVE-2021-3842 is a HIGH (CVSS 7.5) vulnerability affecting nltk, nltk (nltk).
Chance of exploitation in the next 30 days (EPSS): 1.6%, higher than 75.4% of all vulnerabilities.
Fix: update to 3.6.6 or later.

Package	Affected versions	Patched versions
nltk PyPI	`< 3.6.6`	`3.6.6`
nltk nltk	`< 3.6.6`	`3.6.6`

NLTK is vulnerable to REDoS in some RegexpTaggers used in the functions get_pos_tagger and malt_regex_tagger.

NVD description

nltk is vulnerable to Inefficient Regular Expression Complexity

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Package

Affected versions

Patched versions

PyPI

< 3.6.6

3.6.6

< 3.6.6

3.6.6

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