{"id":"CVE-2026-80206","summary":"NLTK 3.10.2 Regular Expression Denial of Service via tgrep","details":"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.","aliases":["GHSA-w3v8-gmh9-3wv7"],"modified":"2026-08-28T11:47:33.450673272Z","published":"2026-08-26T10:28:15.035Z","database_specific":{"cwe_ids":["CWE-1333"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80206.json","cna_assigner":"VulnCheck"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80206.json"},{"type":"ADVISORY","url":"https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80206"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/nltk/nltk","events":[{"introduced":"0"},{"fixed":"303f6e2ba8e4548a5f54fd65d86bb5c9a949f1db"}],"database_specific":{"source":["AFFECTED_FIELD","DESCRIPTION"],"extracted_events":[{"introduced":"0"},{"fixed":"3.10.3"}]}}],"versions":["v3.10.2-rc1","v3.10.2","v3.10.1","v.3.10.1","v3.10.1-rc2","v3.10.0-rc2","v3.10.0","v3.10.1-rc1","v3.10.0-rc1","3.9.4","3.9.3","v3.9.2","3.9.2","3.9.1","3.9","3.8.2","3.8.1","3.8","3.7","3.6.7","3.6.6","3.6.5","3.6.2","3.6.1","3.6","3.5","3.5b1","3.4.4","3.4.3","3.4.1","3.4","3.3","3.2.5","3.2.4","3.2.3","3.2.2","3.2.1","3.2","3.1","3.0.5","3.0.4","3.0.3","3.0.2","3.0.0b1","3.0a4","2.0.1rc4","2.0.1rc3","2.0.1rc2","2.0.1rc1"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-80206.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}]}