Affected: Red Hat build of Keycloak 26.6, Red Hat build of Keycloak 26.6.7, Red Hat Data Grid 8, Red Hat JBoss Enterprise Application Platform Expansion Pack, Red Hat Single Sign-On 7

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.