{"id":"CVE-2026-37977","aliases":["EUVD-2026-19201","GHSA-5v8v-xvjv-57x7"],"status":"published","title":"Keycloak: org.keycloak.protocol.oidc.grants.ciba: keycloak: information disclosure via cors header injection due to unvalidated jwt azp claim","description":"A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the `azp` claim from a client-supplied JSON Web Token (JWT) is used to set the `Access-Control-Allow-Origin` header before the JWT signature is validated. When a specially crafted JWT with an attacker-controlled `azp` value is processed, this value is reflected as the CORS origin, even if the grant is later rejected. This can lead to the exposure of low-sensitivity information from authorization server error responses, weakening origin isolation, but only when a target client is misconfigured with `webOrigins: [\"*\"]`.","severity":{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00258,"percentile":0.17527,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-346"],"published":"2026-04-06T08:38:36Z","modified":"2026-10-26T21:10:00Z","fixes":[{"ecosystem":"Maven","package":"org.keycloak:keycloak-services","fixed_in":["26.4.13","26.6.3"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Maven","package":"org.keycloak:keycloak-services","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"26.4.13"}]}]},{"source":"ghsa","ecosystem":"Maven","package":"org.keycloak:keycloak-services","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"26.5.0"},{"fixed":"26.6.3"}]}]},{"source":"osv","ecosystem":"Maven","package":"org.keycloak:keycloak-services","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"26.4.13"}]}],"versions":["1.0-alpha-1","1.0-alpha-1-12062013","1.0-alpha-2","1.0-alpha-3","1.0-alpha-4","1.0-beta-1","1.0-beta-1-20150521","1.0-beta-1-20150523","1.0-beta-2","1.0-beta-3","1.0-beta-4","1.0-final","1.0-rc-1","1.0-rc-2","1.0.1.Final","1.0.2.Final","1.0.3.Final","1.0.4.Final","1.0.5.Final","1.1.0.Beta1","1.1.0.Beta2","1.1.0.Final","1.1.1.Final","1.2.0.Beta1","1.2.0.CR1","1.2.0.Final","1.3.0.Final","1.3.1.Final","1.4.0.Final","1.5.0-Final","1.5.0.Final","1.5.1.Final","1.6.0.Final","1.6.1.Final","1.7.0.CR1","1.7.0.Final","1.8.0.Alpha1","1.8.0.CR1","1.8.0.CR2","1.8.0.CR3","1.8.0.Final","1.8.1.Final","1.9.0.CR1","1.9.0.Final","1.9.1.Final","1.9.2.Final","1.9.3.Final","1.9.4.Final","1.9.5.Final","1.9.7.Final","1.9.8.Final","10.0.0","10.0.1","10.0.2","11.0.0","11.0.1","11.0.2","11.0.3","12.0.0","12.0.1","12.0.2","12.0.3","12.0.4","13.0.0","13.0.1","14.0.0","15.0.0","15.0.1","15.0.2","15.1.0","15.1.1","16.0.0","16.1.0","16.1.1","17.0.0","17.0.1","18.0.0","18.0.1","18.0.2","19.0.0","19.0.1","19.0.2","19.0.3","2.0.0.CR1","2.0.0.Final","2.1.0.CR1","2.1.0.Final","2.2.0.CR1","2.2.0.Final","2.2.1.Final","2.3.0.CR1","2.3.0.Final","2.4.0.CR1","2.4.0.Final","2.5.0.CR1","2.5.0.Final","2.5.1.Final","2.5.4.Final","2.5.5.Final","20.0.0","20.0.1","20.0.2","20.0.3","20.0.4","20.0.5","21.0.0","21.0.1","21.0.2","21.1.0","21.1.1","21.1.2","22.0.0","22.0.1","22.0.2","22.0.3","22.0.4","22.0.5","23.0.0","23.0.1","23.0.2","23.0.3","23.0.4","23.0.5","23.0.6","23.0.7","24.0.0","24.0.1","24.0.2","24.0.3","24.0.4","24.0.5","25.0.0","25.0.1","25.0.2","25.0.3","25.0.4","25.0.5","25.0.6","26.0.0","26.0.1","26.0.2","26.0.3","26.0.4","26.0.5","26.0.6","26.0.7","26.0.8","26.1.0","26.1.1","26.1.2","26.1.3","26.1.4","26.1.5","26.2.0","26.2.1","26.2.2","26.2.3","26.2.4","26.2.5","26.3.0","26.3.1","26.3.2","26.3.3","26.3.4","26.3.5","26.4.0","26.4.1","26.4.2","26.4.3","26.4.4","26.4.5","26.4.6","26.4.7","3.0.0.CR1","3.0.0.Final","3.1.0.CR1","3.1.0.Final","3.2.0.CR1","3.2.0.Final","3.2.1.Final","3.3.0.CR1","3.3.0.CR2","3.3.0.Final","3.4.0.CR1","3.4.0.Final","3.4.1.CR1","3.4.1.Final","3.4.2.Final","3.4.3.Final","4.0.0.Beta1","4.0.0.Beta2","4.0.0.Beta3","4.0.0.Final","4.1.0.Final","4.2.0.Final","4.2.1.Final","4.3.0.Final","4.4.0.Final","4.5.0.Final","4.6.0.Final","4.7.0.Final","4.8.0.Final","4.8.1.Final","4.8.2.Final","4.8.3.Final","5.0.0","6.0.0","6.0.1","7.0.0","7.0.1","8.0.0","8.0.1","8.0.2","9.0.0","9.0.2","9.0.3"]},{"source":"osv","ecosystem":"Maven","package":"org.keycloak:keycloak-services","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"26.5.0"},{"fixed":"26.6.3"}]}],"versions":["26.5.0","26.5.1","26.5.2","26.5.3","26.5.4","26.5.5","26.5.6","26.5.7","26.6.0","26.6.1","26.6.2"]}],"products":[{"vendor":"red hat","product":"red hat build of keycloak 26.4"},{"vendor":"red hat","product":"red hat build of keycloak 26.4.13"},{"vendor":"red hat","product":"red hat build of keycloak 26.6"},{"vendor":"red hat","product":"red hat build of keycloak 26.6.3"},{"vendor":"redhat","product":"build_of_keycloak"}],"references":[{"url":"https://access.redhat.com/errata/RHSA-2026:25097","tags":["vendor-advisory","x_refsource_REDHAT","web"]},{"url":"https://access.redhat.com/errata/RHSA-2026:25098","tags":["vendor-advisory","x_refsource_REDHAT","web"]},{"url":"https://access.redhat.com/errata/RHSA-2026:30049","tags":["vendor-advisory","x_refsource_REDHAT","web"]},{"url":"https://access.redhat.com/errata/RHSA-2026:30050","tags":["vendor-advisory","x_refsource_REDHAT","web"]},{"url":"https://access.redhat.com/security/cve/CVE-2026-37977","tags":["vdb-entry","x_refsource_REDHAT","Vendor Advisory","web"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2455324","tags":["issue-tracking","x_refsource_REDHAT","Issue Tracking","Vendor Advisory","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-37977","tags":["advisory"]},{"url":"https://github.com/keycloak/keycloak/issues/48036","tags":["web"]},{"url":"https://github.com/keycloak/keycloak/pull/49512","tags":["web"]},{"url":"https://github.com/keycloak/keycloak/commit/1439bd58a9f25b0d28d0400015f49f35f227ce04","tags":["web"]},{"url":"https://github.com/keycloak/keycloak/commit/461ce79a6cd6bfef7ca7fa41da287a3127f47ae4","tags":["web"]},{"url":"https://github.com/keycloak/keycloak/commit/ad34724a5d1ba8b6edf7a2c8c83826b1c20539e7","tags":["web"]},{"url":"https://github.com/advisories/GHSA-5v8v-xvjv-57x7"},{"url":"https://github.com/keycloak/keycloak","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-37977","title":"Keycloak: org.keycloak.protocol.oidc.grants.ciba: keycloak: information disclosure via cors header injection due to unvalidated jwt azp claim","description":"A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the `azp` claim from a client-supplied JSON Web Token (JWT) is used to set the `Access-Control-Allow-Origin` header before the JWT signature is validated. When a specially crafted JWT with an attacker-controlled `azp` value is processed, this value is reflected as the CORS origin, even if the grant is later rejected. This can lead to the exposure of low-sensitivity information from authorization server error responses, weakening origin isolation, but only when a target client is misconfigured with `webOrigins: [\"*\"]`.","status":"published","published":"2026-04-06T08:38:36.657Z","modified":"2026-06-26T07:01:32.805Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low","assessor":"cna"}],"cwes":["CWE-346"],"updated_at":"2026-11-02T13:39:16.730222Z"}],"euvd":[{"id":"EUVD-2026-19201","description":"A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the `azp` claim from a client-supplied JSON Web Token (JWT) is used to set the `Access-Control-Allow-Origin` header before the JWT signature is validated. When a specially crafted JWT with an attacker-controlled `azp` value is processed, this value is reflected as the CORS origin, even if the grant is later rejected. This can lead to the exposure of low-sensitivity information from authorization server error responses, weakening origin isolation, but only when a target client is misconfigured with `webOrigins: [\"*\"]`.","status":"published","published":"2026-04-06T08:38:36Z","modified":"2026-06-26T07:01:32Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"updated_at":"2026-11-02T18:20:24.957062Z"}],"ghsa":[{"id":"GHSA-5v8v-xvjv-57x7","title":"Keycloak vulnerable to information disclosure via CORS header injection due to unvalidated JWT azp claim","description":"A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the `azp` claim from a client-supplied JSON Web Token (JWT) is used to set the `Access-Control-Allow-Origin` header before the JWT signature is validated. When a specially crafted JWT with an attacker-controlled `azp` value is processed, this value is reflected as the CORS origin, even if the grant is later rejected. This can lead to the exposure of low-sensitivity information from authorization server error responses, weakening origin isolation, but only when a target client is misconfigured with `webOrigins: [\"*\"]`.","status":"published","published":"2026-04-06T09:31:42Z","modified":"2026-07-15T18:38:10Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"cwes":["CWE-346"],"updated_at":"2026-11-02T14:40:43.958448Z"}],"nvd":[{"id":"CVE-2026-37977","description":"A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the `azp` claim from a client-supplied JSON Web Token (JWT) is used to set the `Access-Control-Allow-Origin` header before the JWT signature is validated. When a specially crafted JWT with an attacker-controlled `azp` value is processed, this value is reflected as the CORS origin, even if the grant is later rejected. This can lead to the exposure of low-sensitivity information from authorization server error responses, weakening origin isolation, but only when a target client is misconfigured with `webOrigins: [\"*\"]`.","status":"published","published":"2026-04-06T09:16:17.85Z","modified":"2026-10-26T21:10:00.17Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low","assessor":"secondary"},{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-346"],"updated_at":"2026-11-02T14:12:13.1424Z"}],"osv":[{"id":"GHSA-5v8v-xvjv-57x7","title":"Keycloak vulnerable to information disclosure via CORS header injection due to unvalidated JWT azp claim","description":"A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the `azp` claim from a client-supplied JSON Web Token (JWT) is used to set the `Access-Control-Allow-Origin` header before the JWT signature is validated. When a specially crafted JWT with an attacker-controlled `azp` value is processed, this value is reflected as the CORS origin, even if the grant is later rejected. This can lead to the exposure of low-sensitivity information from authorization server error responses, weakening origin isolation, but only when a target client is misconfigured with `webOrigins: [\"*\"]`.","status":"published","published":"2026-04-06T09:31:42Z","modified":"2026-07-15T19:01:07.571326237Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"cwes":["CWE-346"],"updated_at":"2026-11-02T15:46:38.911014Z"}]}}