{"cve":"CVE-2026-63311","nvd":{"published":"2026-08-22T15:16:19.233","modified":"2026-10-14T13:10:00.187","status":"Analyzed","description":"NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validate_network_url() function in nltk/pathsec.py. The _resolve_hostname() helper catches OSError and ValueError during socket.getaddrinfo() and returns an empty list; when DNS resolution fails, the validation loop executes no IP checks and the function fails open, allowing urlopen() to proceed without validation. An attacker who can trigger DNS resolution failures or use DNS rebinding can bypass SSRF protections and reach restricted network resources, including cloud metadata endpoints (e.g., 169.254.169.254).","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L","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:L/A:N","score":5.3},"cwes":["CWE-918"],"references":["https://github.com/nltk/nltk/security/advisories/GHSA-3gqm-fcw5-w839","https://www.vulncheck.com/advisories/nltk-before-ssrf-via-dns-resolution-failure"],"products":["nltk:nltk"],"source":"nvd","synced_at":"2026-10-19T22:49:38.260478770+00:00"},"epss":{"cve":"CVE-2026-63311","score":0.00334,"percentile":0.26568,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-3gqm-fcw5-w839","url":"https://osv.dev/vulnerability/GHSA-3gqm-fcw5-w839","summary":"NLTK: SSRF Fail-Open in validate_network_url() via DNS Resolution Failure","modified":"2026-09-02T16:00:17.562331221Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.0"],"fixed":["3.10.0"]}]},{"id":"PYSEC-2026-3723","url":"https://osv.dev/vulnerability/PYSEC-2026-3723","summary":"","modified":"2026-08-28T02:30:02.703675828Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.0"],"fixed":["3.10.0"]}]}],"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."]}