A flaw was found in the SAML adapter component of Keycloak, which is used to secure applications with SAML-based authentication. The adapter fails to verify that the issuer of a signed SAML assertion matches the expected identity provider configured for the application. If multiple identity providers share the same trusted signing key, an attacker who controls one of those providers can create a validly signed assertion to log into the application as any user, potentially gaining full administrative control.