Vulnerability Description
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: ["*"]`.
CVSS Score
LOW
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Redhat | Build Of Keycloak | - |
Related Weaknesses (CWE)
References
- https://access.redhat.com/security/cve/CVE-2026-37977Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=2455324Issue TrackingVendor Advisory
FAQ
What is CVE-2026-37977?
CVE-2026-37977 is a vulnerability with a CVSS score of 3.7 (LOW). 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 occu...
How severe is CVE-2026-37977?
CVE-2026-37977 has been rated LOW with a CVSS base score of 3.7/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-37977?
Check the references section above for vendor advisories and patch information. Affected products include: Redhat Build Of Keycloak.