{"cve":"CVE-2026-81724","nvd":{"published":"2026-08-27T17:21:03.100","modified":"2026-08-31T19:06:33.930","status":"Analyzed","description":"NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed Python's recursion limit and raise an unhandled RecursionError, crashing applications that parse user-supplied feature structures or feature grammars.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","score":6.9},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","score":5.3},"cwes":["CWE-674"],"references":["https://github.com/nltk/nltk/security/advisories/GHSA-cw6x-m8jw-qmrh","https://www.vulncheck.com/advisories/nltk-before-3.10.3-denial-of-service-via-uncontrolled-recursion","https://github.com/nltk/nltk/security/advisories/GHSA-cw6x-m8jw-qmrh"],"products":["nltk:nltk"],"source":"nvd","synced_at":"2026-10-19T22:50:17.453294893+00:00"},"epss":{"cve":"CVE-2026-81724","score":0.00456,"percentile":0.39589,"date":"2026-11-01"},"kev":null,"osv":[{"id":"GHSA-cw6x-m8jw-qmrh","url":"https://osv.dev/vulnerability/GHSA-cw6x-m8jw-qmrh","summary":"NLTK: Uncontrolled recursion in nltk.featstruct.FeatStructReader causes unhandled RecursionError (DoS) via deeply nested feature-structure input","modified":"2026-09-10T03:51:15.361788366Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.3"],"fixed":["3.10.3"]}]},{"id":"PYSEC-2026-3739","url":"https://osv.dev/vulnerability/PYSEC-2026-3739","summary":"","modified":"2026-09-01T09:15:03.464962431Z","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."]}