CVE-2026-9803: Red Hat Build Of Keycloak

Medium severity, CVSS 5.3. EPSS: 0.7% chance of exploitation in the next 30 days.

A flaw was found in Keycloak's ClientRegistrationAuth component. A remote unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with a malformed 'Authorization: Bearer' header to any client registration endpoint. This can lead to an ArrayIndexOutOfBoundsException, causing the server to return an HTTP 500 error and resulting in a Denial of Service (DoS) for the affected service.

Affected products

• Red Hat Build Of Keycloak: affected versions not specified

Published 2026-05-28. Last modified 2026-06-26.