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.
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Affected Vendors & Products
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Fixes
Solution
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References
History
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 |
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| Weaknesses | CWE-407 | |
| CPEs | cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Nltk
Nltk nltk |
|
| References |
| |
| Metrics |
cvssV3_1
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MITRE
Status: PUBLISHED
Assigner: VulnCheck
Published:
Updated: 2026-08-27T17:49:54.623Z
Reserved: 2026-08-27T11:13:14.064Z
Link: CVE-2026-81722
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-08-27T17:21:02.800
Modified: 2026-08-27T17:21:02.800
Link: CVE-2026-81722
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses