An admin with manage-clients permission, has always access to manage permissions via the permissions client and, therefore, can escalate privileges to assign to him or other admins permissions to manage roles, users or whatever. Right now `manage-clients` is exactly the same than manage-permissions.
Requirements to exploit: The attacker should be a `manage-clients` administrator in keycloak and the realm should be configure with admin permissions (enabled at realm level).
Reproducer
In a keycloak realm enable admin permissions in Realm Settings -> General.

Create an admin user and grant to him manage, view and list clients.