ZDNet:

A security researcher has released today a new jailbreak that impacts all iOS devices running on A5 to A11 chipsets — chips included in all Apple products released between 2011 and 2017, spanning eight generations of devices, from iPhone 4S to iPhone 8 and X.

The jailbreak uses a new exploit named Checkm8 that exploits vulnerabilities in Apple’s Bootrom (secure boot ROM) to grant phone owners full control over their device.

On Twitter, he described Checkm8 as “a permanent unpatchable bootrom exploit,” making the Checkm8 jailbreak one of the most extensive and efficient rooting tools of its kind.

This is moderately bad. It is said to be unpatchable but the attacker needs physical access to your phone and it doesn’t survive a reboot.