So the hack being demonstrated is against a provisioned phone, which requests a secure auth list from the TFTP to authenticate SSH access. The SSH access file

So the hack being demonstrated is against a provisioned phone, which requests a secure auth list from the TFTP to authenticate SSH access. The SSH access file is checksummed and the processor on the phone would be too slow processing this file, so it asks the TFTP server for this. A simple way to lock this down would be MAC filtering, another alternative would be building a secondary auth mechanism into the firmware. Either way, this shouldn't happen. So in answer to your question: there are a lot of things Cisco could do to mitigate this, but they haven't done them for whatever reason. I don't think Cisco is the only guilty party here (these exploits would likely work on many other manufacturers with a little modification), but pretending this isn't a serious exploit is ridiculous.