If enabled, you use a firewire connection. You don't even need to reboot and can connect as root to any running processes and filesystems.
http://www.breaknenter.org/projects/inception/
Yes, that is actual working technology.
http://www.breaknenter.org/projects/inception/
Yes, that is actual working technology.
Just put glue in the firewire connector, you say? Well, for instance most laptops that can be docked are firewire-accessible through the docking port. The firewire interface is also reachable through a USB adapter. So you'd have to glue the USB ports shut as well. (Impractical). Even if you do all this, most motherboards have the FireWire interface enabled on a PCI level, even if there are no physical PCI ports on the computer. So against this attack you'd be pretty much hosed regardless, unless you use a chipset that explicitly doesn't implement FireWire.
Also, FireWire over USB is repeatedly mentioned as not working.