{"cve":"CVE-2026-81722","nvd":{"published":"2026-08-27T17:21:02.800","modified":"2026-08-31T15:44:19.437","status":"Analyzed","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.","cvss_v4":{"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","score":8.7},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-407"],"references":["https://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94g","https://www.vulncheck.com/advisories/nltk-porterstemmer-before-3.10.3-quadratic-time-dos","https://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94g"],"products":["nltk:nltk"],"source":"nvd","synced_at":"2026-10-19T22:50:17.453294893+00:00"},"epss":{"cve":"CVE-2026-81722","score":0.00521,"percentile":0.44267,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-ww6m-cw3f-q94g","url":"https://osv.dev/vulnerability/GHSA-ww6m-cw3f-q94g","summary":"NLTK: Quadratic-time DoS in PorterStemmer via long runs of 'y'","modified":"2026-09-10T03:50:54.572733114Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.3"],"fixed":["3.10.3"]}]},{"id":"PYSEC-2026-3738","url":"https://osv.dev/vulnerability/PYSEC-2026-3738","summary":"","modified":"2026-09-01T09:15:04.064770060Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.3"],"fixed":["3.10.3"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}