CVE-2026-37977
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk17th percentile — higher than 17% of all known CVEs
Summary
A flaw was found in Keycloak where a remote attacker can exploit a CORS header injection vulnerability in the UMA token endpoint. The `azp` claim from a client-supplied JWT is used to set the `Access-Control-Allow-Origin` header before signature validation, allowing reflection of attacker-controlled values. This only affects clients misconfigured with `webOrigins: ["*"]`.
Risk Assessment
The risk involves potential exposure of low-sensitivity information from authorization server error responses and weakened origin isolation, which could facilitate further attacks, but only when a target client is misconfigured.
Recommendation
It is recommended to immediately update Keycloak to a patched version and review client configurations to avoid using `webOrigins: ["*"]` unless strictly necessary.
Original NVD description (English source)
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: ["*"]`.