Executive brief
Keycloak, an open-source identity and access management solution, is vulnerable to a denial-of-service attack. By sending a specifically malformed authorization request, an unauthenticated attacker can cause the server to crash or return errors. This disrupts the ability of users and applications to log in or register, potentially halting business operations that rely on Keycloak for authentication.
Technical details
An out-of-bounds read vulnerability (CWE-125) exists in Keycloak's ClientRegistrationAuth component within the keycloak-services package. The flaw is triggered when the server processes a POST request containing a malformed 'Authorization: Bearer' header at any client registration endpoint. This malformed input leads to an ArrayIndexOutOfBoundsException, resulting in an HTTP 500 error. A remote, unauthenticated attacker can exploit this to cause a Denial of Service (DoS) condition. The issue is addressed in Keycloak version 26.6.3 and corresponding Red Hat builds.
Affected products
- Keycloak Keycloak <= 26.4.7, >= 26.5.0, < 26.6.3
- Red Hat Red Hat build of Keycloak 26.4, 26.6
Timeline
- 2026-05-28: disclosed
- 2026-05-28: advisory
- 2026-06-10: patched: Red Hat release 26.6.3 published