{"id":"CVE-2026-37977","title":"A flaw was found in Keycloak","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. This flaw occurs because the `azp` claim from a cli…","severity":"low","cvss":3.7,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","cwe":["CWE-346"],"published":"2026-04-06","updated":"2026-06-26","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-37977","references":[{"url":"https://access.redhat.com/errata/RHSA-2026:25097","label":"secalert@redhat.com"},{"url":"https://access.redhat.com/errata/RHSA-2026:25098","label":"secalert@redhat.com"},{"url":"https://access.redhat.com/errata/RHSA-2026:30049","label":"secalert@redhat.com"},{"url":"https://access.redhat.com/errata/RHSA-2026:30050","label":"secalert@redhat.com"},{"url":"https://access.redhat.com/security/cve/CVE-2026-37977","label":"secalert@redhat.com"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2455324","label":"secalert@redhat.com"}],"tags":["nvd"],"epss":0.00253,"epssPercentile":0.1709,"ingestedAt":"2026-06-26T16:43:13.622Z","slug":"CVE-2026-37977","body":"## Overview\n\nA 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: [\"*\"]`.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":20,"depthScoreParts":{"impact":20.4,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}