Algorithmic Complexity Affecting nltk package, versions <3.10.3-1


Severity

Recommended
0.0
high
0
10

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Threat Intelligence

EPSS
0.36% (30th percentile)

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  • Snyk IDSNYK-DEBIANUNSTABLE-NLTK-19385606
  • published28 Aug 2026
  • disclosed27 Aug 2026

Introduced: 27 Aug 2026

NewCVE-2026-81722  (opens in a new tab)
CWE-407  (opens in a new tab)

How to fix?

Upgrade Debian:unstable nltk to version 3.10.3-1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream nltk package and not the nltk package as distributed by Debian. See How to fix? for Debian:unstable relevant fixed versions and status.

nltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem(). The _is_consonant() helper walks backward over the entire run of trailing 'y' characters on every call, and _measure() invokes it for each stem position, causing O(n^2) behavior. A single ~20-50 KB untrusted token consisting of a long run of the letter 'y' followed by a matching suffix (e.g., 'ness') can pin a CPU core for seconds to minutes, causing availability impact.

CVSS Base Scores

version 3.1