{"id":"CVE-2026-37977","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-37977","summary":"Keycloak vulnerable to information disclosure via CORS header injection due to unvalidated JWT azp claim","details":"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: [\"*\"]`.","published":"2026-04-06T09:31:42Z","modified":"2026-07-15T19:01:07.571326237Z","cvss":{"score":3.7,"severity":"LOW","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Maven","name":"org.keycloak:keycloak-services","fixedVersion":"26.4.13"},{"ecosystem":"Maven","name":"org.keycloak:keycloak-services","fixedVersion":"26.6.3"}],"fix":{"url":"https://github.com/keycloak/keycloak/pull/49512","label":"keycloak/keycloak#49512"},"references":[{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-37977"},{"type":"WEB","url":"https://github.com/keycloak/keycloak/issues/48036"},{"type":"WEB","url":"https://github.com/keycloak/keycloak/pull/49512"},{"type":"WEB","url":"https://github.com/keycloak/keycloak/commit/1439bd58a9f25b0d28d0400015f49f35f227ce04"},{"type":"WEB","url":"https://github.com/keycloak/keycloak/commit/461ce79a6cd6bfef7ca7fa41da287a3127f47ae4"},{"type":"WEB","url":"https://github.com/keycloak/keycloak/commit/ad34724a5d1ba8b6edf7a2c8c83826b1c20539e7"},{"type":"WEB","url":"https://access.redhat.com/errata/RHSA-2026:25097"},{"type":"WEB","url":"https://access.redhat.com/errata/RHSA-2026:25098"},{"type":"WEB","url":"https://access.redhat.com/errata/RHSA-2026:30049"},{"type":"WEB","url":"https://access.redhat.com/errata/RHSA-2026:30050"},{"type":"WEB","url":"https://access.redhat.com/security/cve/CVE-2026-37977"},{"type":"WEB","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2455324"},{"type":"PACKAGE","url":"https://github.com/keycloak/keycloak"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-15T19:01:07.571326237Z"}}