BSD Today has this advisory: "If agent or X11 forwarding is disabled in the ssh client configuration, the client does not request these features
during session setup. This is the correct behaviour.
However, when the ssh client receives an actual request asking for access to the ssh-agent, the client fails to
check whether this feature has been negotiated during session setup. The client does not check whether the
request is in compliance with the client configuration and grants access to the ssh-agent. A similar problem
exists in the X11 forwarding implementation."