CVE-2026-81722

HighCVSS 7.5

Published: 27/08/2026(UTC)Updated: 27/08/2026(UTC)Translated: 27/08/2026(UTC)NVD NIST

Summary

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.

Risk Assessment

An attacker can cause CPU exhaustion and denial of service, potentially affecting the availability of applications using NLTK.

Recommendation

Update NLTK to version 3.10.3 or later, which contains the fix.

Original NVD description (English source)

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.