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: ["*"]`.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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: ["*"]`. (CVE-2026-37977)

ID	Name	Product	Family	Type	Severity
458373	Echo: org.keycloak:keycloak-services: security update to 26.4.13	Tenable Cloud Security	Echo Local Security Checks	Local	medium
458373	Echo: org.keycloak:keycloak-services: security update to 26.4.13	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	medium
444751	SCA: security update for org.keycloak:keycloak-services (GHSA-5v8v-xvjv-57x7)	Tenable Cloud Security	SCA Checks	Local	medium
444751	SCA: security update for org.keycloak:keycloak-services (GHSA-5v8v-xvjv-57x7)	Tenable Self-Hosted Container Security	SCA Checks	Local	medium

Detections

Analytics

CVE-2026-37977

medium

Tenable Plugins

medium

medium

medium

medium