{"affected":[{"package":{"ecosystem":"Hex","name":"ash_authentication_oauth2_server","purl":"pkg:hex/ash_authentication_oauth2_server"},"ranges":[{"events":[{"introduced":"0.1.3"},{"fixed":"0.3.1"}],"type":"SEMVER"}],"versions":["0.1.3","0.2.0","0.2.1","0.2.2","0.3.0"]},{"ranges":[{"events":[{"introduced":"99de0a1cacb5ef667c4533278b7c81ca98c00231"},{"fixed":"09f97476715da031b136eaec7b2cda2363ad8149"}],"repo":"https://github.com/ash-project/ash_authentication_oauth2_server","type":"GIT"}]}],"aliases":["GHSA-2h3v-83jg-2qmm","CVE-2026-82756"],"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"}],"database_specific":{"capec_ids":["CAPEC-153"],"cpe_ids":["cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-116"]},"details":"## Summary\n\nImproper Encoding or Escaping of Output vulnerability in ash-project ash\\_authentication\\_oauth2\\_server allows an unauthenticated attacker to inject arbitrary authentication parameters into the WWW-Authenticate challenge header.\n\nBearerPlug and RequireScopePlug built the Bearer resource\\_metadata=\"...\" challenge by interpolating a resource\\_metadata URL derived from the request tenant directly into the quoted value. In a multi-tenant application that sets the Ash tenant from request-controlled data (a subdomain, the Host, a path segment, or a header), a tenant containing a \" closes the quoted value and appends attacker-chosen auth-params, including a second resource\\_metadata URL pointing at an attacker-controlled authorization server that spec-following clients follow. Carriage returns and line feeds are rejected by Plug, so this is parameter injection within one header, not response splitting.\n\nThis issue affects ash\\_authentication\\_oauth2\\_server: from 0.1.3 before 0.3.1.\n\n## Configuration\n\nReachable only in a multi-tenant application that derives the Ash tenant from request-controlled input (subdomain, Host, path, or header) and uses BearerPlug or RequireScopePlug; the tenant reaches the challenge through the server's tenant-aware resource\\_url.","id":"EEF-CVE-2026-82756","modified":"2026-09-07T22:30:55.757407Z","published":"2026-09-07T22:30:55.280Z","references":[{"type":"ADVISORY","url":"https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-82756.html"},{"type":"FIX","url":"https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149"},{"type":"PACKAGE","url":"https://hex.pm/packages/ash_authentication_oauth2_server"}],"related":[],"schema_version":"1.7.3","severity":[{"score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N","type":"CVSS_V4"}],"summary":"ash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injection","upstream":[]}