Fusee Gelee (translates to Frozen Rocket) is a coldboot launcher. The exploit takes advantage of a USB software stack that is provided inside the BootROM. ... By creating your own USB control request, attacks can use this vulnerability to gain control of the Boot and Power Management Processor (BPMP).

Does Fusee gelee work on all switches?

If it were possible to apply patches to the bootrom after a unit had been shipped, anyone with a sufficiently powerful exploit would be able to make their own patches, bypassing boot security. It also means that any Switch currently affected will continue to be able to use Fusée Gelée throughout its life.

How does the Switch exploit work?

The exploit involves kicking the Switch into USB recovery mode by shorting a pin on the right-hand Joy-Con connector. A payload is then sent at a crucial point during a USB check, forcing the system to "request up to 65,535 bytes per control request," much more than it can handle.