{"id":"EEF-CVE-2026-82757","summary":"ash_authentication_oauth2_server CIMD fetcher classifies IPv4-in-IPv6 and site-local addresses as public, allowing SSRF","details":"## Summary\n\nServer-Side Request Forgery (SSRF) vulnerability in ash-project ash_authentication_oauth2_server allows an attacker who controls a client metadata URL and its DNS to make the server connect to internal or loopback addresses.\n\n`public_ip?/1` in `AshAuthentication.Oauth2Server.CIMD.ReqFetcher` enforces the outbound policy for CIMD metadata fetches. It classified several address forms as publicly routable that are not: IPv4-compatible `::/96` (for example `::127.0.0.1`), SIIT IPv4-translated `::ffff:0:0:0/96`, and deprecated site-local `fec0::/10`. A returned AAAA record in one of these ranges passed the policy, so a fetch pinned to that address reached space the policy was meant to block.\n\nThis issue affects ash_authentication_oauth2_server: from 0.3.0 before 0.3.1.\n\n## Configurations\n\nReachable only when Client ID Metadata Documents are enabled (`cimd_enabled?: true`), so the authorize endpoint fetches attacker-suppliable metadata URLs, and an internal or loopback target resolves to one of the affected IPv6 address forms.","aliases":["CVE-2026-82757","GHSA-wprp-8gvj-p6cv"],"modified":"2026-09-08T22:45:02.745057660Z","published":"2026-09-07T22:31:34.656Z","database_specific":{"cwe_ids":["CWE-918"],"capec_ids":["CAPEC-664"],"cpe_ids":["cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*"]},"references":[{"type":"ADVISORY","url":"https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-wprp-8gvj-p6cv"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-82757.html"},{"type":"FIX","url":"https://github.com/ash-project/ash_authentication_oauth2_server/commit/268b591261a3473ab9b87272963e4dd2fd99d972"},{"type":"PACKAGE","url":"https://hex.pm/packages/ash_authentication_oauth2_server"}],"affected":[{"package":{"name":"ash_authentication_oauth2_server","ecosystem":"Hex","purl":"pkg:hex/ash_authentication_oauth2_server"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.3.0"},{"fixed":"0.3.1"}]}],"versions":["0.3.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-82757.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/ash-project/ash_authentication_oauth2_server","events":[{"introduced":"e713a9ba816761140c226e2ca55b75c0b93f5984"},{"fixed":"268b591261a3473ab9b87272963e4dd2fd99d972"}]}],"versions":["v0.3.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-82757.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N"}],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Peter Ullrich","type":"REPORTER"},{"name":"Zach Daniel / Ash Project","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"COORDINATOR"}]}