CVE-2026-37977

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 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: ["*"].

Affected Software

VendorProductVersion RangeStatus
Red HatRed Hat build of Keycloak 26.426.4.13-1 < *unaffected
Red HatRed Hat build of Keycloak 26.426.4-19 < *unaffected
Red HatRed Hat build of Keycloak 26.426.4-19 < *unaffected
Red HatRed Hat build of Keycloak 26.626.6.3-3 < *unaffected
Red HatRed Hat build of Keycloak 26.626.6-6 < *unaffected
Red HatRed Hat build of Keycloak 26.626.6-6 < *unaffected

Weaknesses

  • CWE-346: Origin Validation Error

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References