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.
History

Tue, 01 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-606
References
Metrics threat_severity

None

threat_severity

Important


Thu, 27 Aug 2026 18:00:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 27 Aug 2026 16:45:00 +0000

Type Values Removed Values Added
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.
Title nltk PorterStemmer before 3.10.3 Quadratic-time DoS
First Time appeared Nltk
Nltk nltk
Weaknesses CWE-407
CPEs cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*
Vendors & Products Nltk
Nltk nltk
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published: 2026-08-27T14:51:15.857Z

Updated: 2026-08-27T17:49:54.623Z

Reserved: 2026-08-27T11:13:14.064Z

Link: CVE-2026-81722

cve-icon Vulnrichment

Updated: 2026-08-27T17:49:23.759Z

cve-icon NVD

Status : Analyzed

Published: 2026-08-27T17:21:02.800

Modified: 2026-08-31T15:44:19.437

Link: CVE-2026-81722

cve-icon Redhat

Severity : Important

Publid Date: 2026-08-27T14:51:15Z

Links: CVE-2026-81722 - Bugzilla