{"cve":"CVE-2026-80206","nvd":{"published":"2026-08-26T11:16:40.103","modified":"2026-09-01T20:07:46.190","status":"Analyzed","description":"NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","score":8.2},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H","score":5.9},"cwes":["CWE-1333"],"references":["https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7","https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep","https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7"],"products":["nltk:nltk"],"source":"nvd","synced_at":"2026-10-19T22:50:17.453294893+00:00"},"epss":{"cve":"CVE-2026-80206","score":0.0044,"percentile":0.38294,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-w3v8-gmh9-3wv7","url":"https://osv.dev/vulnerability/GHSA-w3v8-gmh9-3wv7","summary":"NLTK: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions","modified":"2026-09-08T20:45:04.333988177Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.3"],"fixed":["3.10.3"]}]},{"id":"PYSEC-2026-3751","url":"https://osv.dev/vulnerability/PYSEC-2026-3751","summary":"","modified":"2026-09-02T09:00:05.019508486Z","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."]}