{"id":"CVE-2026-82756","state":"PUBLISHED","title":"ash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injection","description":"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.","publishedAt":"2026-09-07T22:30:55.280Z","updatedAt":"2026-09-08T14:43:33.571Z","severity":{"score":6.3,"label":"Medium","version":"4.0","vector":"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","source":"EEF"},"assigner":"EEF","products":["ash-project ash_authentication_oauth2_server"],"affected":[{"vendor":"ash-project","product":"ash_authentication_oauth2_server","packageName":"ash_authentication_oauth2_server","packageURL":"pkg:hex/ash_authentication_oauth2_server","defaultStatus":"unaffected","versions":[{"version":"0.1.3","status":"affected","lessThan":"0.3.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug'","'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug'"],"programFiles":["lib/ash_authentication_phoenix/oauth2_server/bearer_plug.ex","lib/ash_authentication_phoenix/oauth2_server/require_scope_plug.ex"],"programRoutines":[{"name":"'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug':call/2"},{"name":"'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug':call/2"}],"repo":"https://github.com/ash-project/ash_authentication_oauth2_server"},{"vendor":"ash-project","product":"ash_authentication_oauth2_server","packageName":"ash-project/ash_authentication_oauth2_server","packageURL":"pkg:github/ash-project/ash_authentication_oauth2_server","defaultStatus":"unaffected","versions":[{"version":"99de0a1cacb5ef667c4533278b7c81ca98c00231","status":"affected","lessThan":"09f97476715da031b136eaec7b2cda2363ad8149","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug'","'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug'"],"programFiles":["lib/ash_authentication_phoenix/oauth2_server/bearer_plug.ex","lib/ash_authentication_phoenix/oauth2_server/require_scope_plug.ex"],"programRoutines":[{"name":"'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug':call/2"},{"name":"'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug':call/2"}],"repo":"https://github.com/ash-project/ash_authentication_oauth2_server"}],"references":["https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm","https://cna.erlef.org/cves/CVE-2026-82756.html","https://osv.dev/vulnerability/EEF-CVE-2026-82756","https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149"],"weaknesses":["CWE-116"],"ingestedAt":"2026-10-29T20:13:15.269Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/82xxx/CVE-2026-82756.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-82756","state":"PUBLISHED","datePublished":"2026-09-07T22:30:55.280Z","dateUpdated":"2026-09-08T14:43:33.571Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-08-31T01:00:10.817Z"},"containers":{"cna":{"title":"ash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injection","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"ash-project","product":"ash_authentication_oauth2_server","packageName":"ash_authentication_oauth2_server","packageURL":"pkg:hex/ash_authentication_oauth2_server","defaultStatus":"unaffected","versions":[{"version":"0.1.3","status":"affected","lessThan":"0.3.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug'","'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug'"],"programFiles":["lib/ash_authentication_phoenix/oauth2_server/bearer_plug.ex","lib/ash_authentication_phoenix/oauth2_server/require_scope_plug.ex"],"programRoutines":[{"name":"'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug':call/2"},{"name":"'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug':call/2"}],"repo":"https://github.com/ash-project/ash_authentication_oauth2_server"},{"vendor":"ash-project","product":"ash_authentication_oauth2_server","packageName":"ash-project/ash_authentication_oauth2_server","packageURL":"pkg:github/ash-project/ash_authentication_oauth2_server","defaultStatus":"unaffected","versions":[{"version":"99de0a1cacb5ef667c4533278b7c81ca98c00231","status":"affected","lessThan":"09f97476715da031b136eaec7b2cda2363ad8149","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug'","'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug'"],"programFiles":["lib/ash_authentication_phoenix/oauth2_server/bearer_plug.ex","lib/ash_authentication_phoenix/oauth2_server/require_scope_plug.ex"],"programRoutines":[{"name":"'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug':call/2"},{"name":"'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug':call/2"}],"repo":"https://github.com/ash-project/ash_authentication_oauth2_server"}],"references":[{"url":"https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm","tags":["vendor-advisory","related"]},{"url":"https://cna.erlef.org/cves/CVE-2026-82756.html","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-82756","tags":["related"]},{"url":"https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149","tags":["patch"]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":6.3,"baseSeverity":"MEDIUM","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"LOW","subIntegrityImpact":"LOW","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"LOW","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-116","description":"CWE-116 Improper Encoding or Escaping of Output","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-09-07T22:30:55.280Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>Reachable only in a multi-tenant application that derives the Ash tenant from request-controlled input (subdomain, <code>Host</code>, path, or header) and uses <code>BearerPlug</code> or <code>RequireScopePlug</code>; 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