CVE-2026-9803 – Keycloak: keycloak: denial of service via malformed authorization header

CVE ID :CVE-2026-9803

Published : May 28, 2026, 6:16 a.m. | 15 minutes ago

Description :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.

Severity: 5.3 | MEDIUM

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