Fusée Gelée is unpatchable
At the technical level, Fusée Gelée is nothing more than a trivial buffer overflow vulnerability. The problem is its location in the Switch's bootROM component —found inside the Nvidia Tegra chipset— that controls the device's boot-up routine.
This component is locked down at the hardware level after leaving the Nintendo factories, meaning they can't be updated via a firmware patch. This makes Fusée Gelée unpatchable, and it's hard to believe Nintendo will recall millions of gaming consoles just to fix a jailbreak.
Exploitation requires forcing Switch in USB recovery mode
Exploiting Fusée Gelée isn't that complicated either, albeit dangerous. Users need to force the Switch to reboot in USB recovery mode and then use the USB connection to launch a Python script via a console.
Probably the hardest part of the entire hack is forcing the Switch into USB recovery mode, which can be achieved by pressing and shorting two pins on the right Joy-Con connector.
Katherine Temkin, the hacker who discovered the exploit, has published
a FAQ page about Fusée Gelée, how users could
short the two pins, and
the PoC code.
The current PoC code only prints device specific data on the Switch's
screen, but Temkin promised to publish more scripts and information about exploiting Fusée Gelée on June 15, 2018, when the original disclosure of this vulnerability was planned to take place.