{"cve":"CVE-2026-66393","nvd":{"published":"2026-08-22T15:16:19.633","modified":"2026-10-14T13:10:00.187","status":"Analyzed","description":"NLTK versions before 3.9.4 contain an unbounded recursion vulnerability in JSONTaggedDecoder.decode_obj() that allows attackers to cause denial of service by supplying deeply nested JSON structures. Attackers can craft JSON payloads exceeding the recursion limit to trigger an unhandled RecursionError that crashes the Python process.","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-674"],"references":["https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw","https://www.vulncheck.com/advisories/nltk-before-denial-of-service-via-jsontaggeddecoder","https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw"],"products":["nltk:nltk"],"source":"nvd","synced_at":"2026-10-19T22:49:38.260478770+00:00"},"epss":{"cve":"CVE-2026-66393","score":0.00521,"percentile":0.43961,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-rf74-v2fm-23pw","url":"https://osv.dev/vulnerability/GHSA-rf74-v2fm-23pw","summary":"Natural Language Toolkit (NLTK) has unbounded recursion in JSONTaggedDecoder.decode_obj() may cause DoS","modified":"2026-09-10T03:50:40.818763364Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.9.4"],"fixed":["3.9.4"]}]},{"id":"PYSEC-2026-3724","url":"https://osv.dev/vulnerability/PYSEC-2026-3724","summary":"","modified":"2026-08-28T02:30:02.708784842Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.9.4"],"fixed":["3.9.4"]}]}],"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."]}