{"id":"CVE-2026-12372","summary":"Server-Side Request Forgery (SSRF) in nltk/nltk","details":"A Server-Side Request Forgery (SSRF) vulnerability exists in nltk/nltk versions 3.9.4 and the current develop branch. The `nltk.pathsec.validate_network_url()` function, intended to prevent SSRF by rejecting internal network addresses, fails to reject IPs in the RFC 6598 shared address space (`100.64.0.0/10`). This occurs because Python's `ipaddress` module does not classify such addresses as `is_private` or `is_global`, and the current guard only checks `is_private` and a few explicit categories. An attacker who can influence a URL passed to NLTK's network-loading helpers can exploit this vulnerability to make a strict-mode application send requests to shared-address-space hosts, potentially exposing non-public infrastructure reachable from the application host. The impact is limited to SSRF-style confidentiality exposure, with no code execution claimed.","aliases":["PYSEC-2026-3955"],"modified":"2026-09-10T13:11:08.397705131Z","published":"2026-08-09T22:45:52.799Z","related":["openSUSE-SU-2026:11510-1"],"database_specific":{"cwe_ids":["CWE-918"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/12xxx/CVE-2026-12372.json","cna_assigner":"@huntr_ai"},"references":[{"type":"WEB","url":"https://huntr.com/bounties/2911b643-571c-42e4-b0c2-9a1fa6f491db"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/12xxx/CVE-2026-12372.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-12372"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/nltk/nltk","events":[{"introduced":"ad9c96ba00a16923ffe917eacf63f1707bfa2d08"},{"last_affected":"ad9c96ba00a16923ffe917eacf63f1707bfa2d08"}],"database_specific":{"cpe":"cpe:2.3:a:nltk:nltk:3.9.4:*:*:*:*:*:*:*","extracted_events":[{"introduced":"3.9.4"},{"last_affected":"3.9.4"}],"source":"CPE_STRING"}}],"versions":["3.9.4"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-12372.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N"}]}