Last week, a report from 404 Media highlighted concerns among law enforcement officials about iPhones automatically rebooting.
While law enforcement officials incorrectly assumed that iPhones were secretly communicating with each other to reboot, this is not actually the case. Instead, Apple added a new security feature in iOS 18.1 that forces iPhones to reboot after a period of inactivity.
The change was first pointed out by security researcher Jiska Klassen on Mastodon. According to Klassen, this “Idle Reboot” feature is designed to automatically reboot an iPhone if it has not been unlocked for a certain period of time.
According to a subsequent report from 404 Media, citing comments from Corellium founder Chris Wade, the reboot occurs after four days. This means that any time an iPhone is not used for more than four days, it will automatically reboot.
The change has caused frustration among police officers, who say it makes iPhones stored for forensic examination more difficult to unlock. After a reboot, the iPhone goes into a pre-first-unlock (BFU) state, making it significantly more difficult to unlock. It’s usually easiest to unlock, or “jailbreak,” an iPhone in the “After First Unlock” state.
But while reports so far have mostly focused on the change’s impact on law enforcement, it will also create another layer of protection against thieves and other bad actors.
Matthew Green, a cryptographer and associate professor at Johns Hopkins University, noted in a statement to 404 Media:
“Remember, the real threat here isn’t the police. It’s the people who would steal your iPhone with malicious intent.” This feature means that if your phone is stolen, thieves won’t be able to babysit it for months until they develop the technology to crack it. I’d argue that rebooting after a reasonable period of inactivity probably won’t inconvenience anyone, but it will make your phone a lot more secure. So that seems like a pretty good idea.”
Apple hasn't commented on the change, but you can view the relevant code changes in iOS 18.1 on GitHub.
