Vulnerability Details CVE-2026-37977
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: ["*"]`.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 0.9%
CVSS Severity
CVSS v3 Score 3.7
References
Products affected by CVE-2026-37977
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cpe:2.3:a:redhat:build_of_keycloak:-