{"cve":"CVE-2026-81725","nvd":{"published":"2026-08-27T17:21:03.247","modified":"2026-09-01T20:06:33.420","status":"Analyzed","description":"NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the read_block method through public APIs like words() and tagged_words() to force repeated rescans and achieve near-quadratic runtime growth.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","score":6.3},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L","score":3.7},"cwes":["CWE-400"],"references":["https://github.com/nltk/nltk/security/advisories/GHSA-8mpw-7fpc-4gqj","https://www.vulncheck.com/advisories/nltk-before-3.10.3-regular-expression-denial-of-service-via-pl196xcorpusreader"],"products":["nltk:nltk"],"source":"nvd","synced_at":"2026-10-19T22:50:17.453294893+00:00"},"epss":{"cve":"CVE-2026-81725","score":0.00369,"percentile":0.30785,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-8mpw-7fpc-4gqj","url":"https://osv.dev/vulnerability/GHSA-8mpw-7fpc-4gqj","summary":"NLTK: Pl196xCorpusReader has quadratic ReDoS on malformed TEI blocks","modified":"2026-09-08T20:45:04.346016767Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.3"],"fixed":["3.10.3"]}]},{"id":"PYSEC-2026-3752","url":"https://osv.dev/vulnerability/PYSEC-2026-3752","summary":"","modified":"2026-09-02T09:00:06.141358767Z","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."]}