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CVE-2026-81722 Details

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.

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:7.5 HIGHVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94g	CISA-ADP	ExploitVendor Advisory
https://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94g	[email protected]	ExploitVendor Advisory
https://www.vulncheck.com/advisories/nltk-porterstemmer-before-3.10.3-quadratic-time-dos	[email protected]	Third Party Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-407	Inefficient Algorithmic Complexity	[email protected]

Affected Products

Product	Versions
nltk nltk	< 3.10.3
CPE cpe:2.3:a:nltk:nltk:::::::: Remediation No remediation found in references.

Change History

3 change records found show changes

Date	Action	Recorded By
Aug 31, 2026	Initial Analysis	[email protected]
Aug 27, 2026	CVE Modified	CISA-ADP
Aug 27, 2026	New CVE Received	[email protected]