{"id":"CVE-2026-82756","summary":"ash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injection","details":"Improper 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.","aliases":["EEF-CVE-2026-82756","GHSA-2h3v-83jg-2qmm"],"modified":"2026-09-10T03:30:53.107376984Z","published":"2026-09-07T22:30:55.280Z","database_specific":{"cwe_ids":["CWE-116"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82756.json","unresolved_ranges":[{"extracted_events":[{"introduced":"99de0a1cacb5ef667c4533278b7c81ca98c00231"},{"fixed":"09f97476715da031b136eaec7b2cda2363ad8149"}],"source":"AFFECTED_FIELD"}],"cna_assigner":"EEF"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-82756.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-82756"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82756.json"},{"type":"ADVISORY","url":"https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-82756"},{"type":"FIX","url":"https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149"},{"type":"PACKAGE","url":"https://github.com/ash-project/ash_authentication_oauth2_server"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ash-project/ash_authentication_oauth2_server","events":[{"introduced":"34ecef8343573572a10fd1587d40032be54df05b"},{"fixed":"15bde4311e31c925a428f34c02b283307619e2a2"},{"fixed":"09f97476715da031b136eaec7b2cda2363ad8149"}],"database_specific":{"source":["DESCRIPTION","REFERENCES"],"extracted_events":[{"introduced":"0.1.3"},{"fixed":"0.3.1"}]}}],"versions":["v0.3.0","v0.2.2","v0.2.1","v0.2.0","v0.1.3"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-82756.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:L/VA:N/SC:L/SI:L/SA:N"}]}