CVE-2026-37977

[CVE catalog]

Severity

Low · CVSS 3.7CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Published

Apr 6, 2026, 8:34:01 AM UTC

Source

[NVD] · [CVE record]

EPSS

0.25% · Oct 27, 2026

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: ["*"]`. keycloak: org.keycloak.protocol.oidc.grants.ciba: Keycloak: Information disclosure via CORS header injection due to unvalidated JWT azp claim Low impact: This vulnerability in Keycloak's UMA token endpoint allows for CORS header injection when a client is misconfigured with `webOrigins: ["*"]`. This can lead to the exposure of low-sensitivity information from authorization server error responses. Exploitation requires a specific client misconfiguration and does not affect default Keycloak installations. The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.