The exploit affects iOS devices with A5 to A11 chips, and is notably the first publicly released bootrom since 2010’s iPhone 4. Checkm8 is a non-patchable, permanent jailbreak procedure that could affect millions of devices. Moreover, the read-only aspect of the exploit means Apple will not be able to patch it with a software update.
The bootrom has other features, including the ability to downgrade iOS versions, running custom firmware and a dual-booting iOS.
The last known bootrom exploit was from George Hotz, or otherwise known as ‘geohot’ who released ‘limera1n’ about 10 years ago. iOS devices that had A4 chips and below, including the 3rd and 4th gen iPod Touch, the original iPad and the iPhone 4 and 3GS were supported.