asterisk -- SIP request can change address of a SIP peer

The Asterisk project reports:

A SIP request can be sent to Asterisk that can change
a SIP peers IP address. A REGISTER does not need to occur,
and calls can be hijacked as a result. The only thing
that needs to be known is the peers name; authentication
details such as passwords do not need to be known. This
vulnerability is only exploitable when the nat option is
set to the default, or auto_force_rport.