The worst part of that is that you can't even configure your host firewall to block it, since the OS it runs on won't be running during the boot, obviously. It has to be blocked upstream. Which means that if you just have one host at a hosting provider, you depend on them to do it (although, you may still have the option to access your BIOS settings to disable PXE, or your host provider may provide upstream firewall configuration).

What we _can_ do, though, while the OS is running is detecting that bogus large ICMP packets are sent continuously. At least, this would be early warning that a reboot may be risky without disabling PXE.