CVE-2026-81722

nltk PorterStemmer before 3.10.3 Quadratic-time DoS

Published: Aug 27, 2026Updated: Aug 31, 2026 Sources: CVE List NVDCWE-407

7.5HIGH

Description

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.

No summary for this CVE yet.

CVSS Vector Breakdown

Exploitability

AV:NAttack Vector

Network

AC:LAttack Complexity

Low

PR:NPrivileges Required

None

UI:NUser Interaction

None

Scope

S:UScope

Unchanged

Impact

C:NConfidentiality

None

I:NIntegrity

None

A:HAvailability

High

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Weaknesses

CWE-407

Affected Products

nltk

oss-projectaka nltk/nltk

nltkLibrary

AI / ML / ml-framework

Exploitability

Official Patch Available

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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

1 technique

Impact

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References

https://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94g

github.com

https://www.vulncheck.com/advisories/nltk-porterstemmer-before-3.10.3-quadratic-time-dos

vulncheck.com

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