CVE-2026-37977
Last modified
CVE-2026-37977 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. 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. EPSS estimates a 0.25% chance of exploitation in the next 30 days.
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: ["*"]`.
Metrics
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Redhat | Build Of Keycloak | All versions |
References
- https://access.redhat.com/security/cve/CVE-2026-37977Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=2455324Issue Tracking, Vendor Advisory
Timeline
- Published
- Last Modified
- Status
- Modified
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