{"id":"CVE-2026-37977","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-37977","summary":"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.…","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":"2026-04-06T09:16:17.850","modified":"2026-06-26T08:16:22.157","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":[],"fix":null,"references":[{"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":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-37977"},{"type":"ADVISORY","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2455324"}],"provenance":{"sources":["OSV.dev","NVD","FIRST.org (EPSS)"],"lastVerified":"2026-06-26T08:16:22.157"}}