Apple indeed added a feature called “inactivity reboot” in iOS 18.1 that reboots locked devices

Apple iOS supports a new feature that reboots locked devices after extended inactivity, aiming to enhance data security for users.

Apple ‘quietly’ implemented a new security feature that automatically reboots a locked device if it has not been used for several days.

The new feature was introduced with the release of iOS 18.1 at the end of October.

The IT giant has implemented an auto-reboot timer on iOS devices that triggers after several days of inactivity. The feature erases sensitive data from memory to prevent unauthorized extraction.

The auto-reboot feature returns devices to a “Before First Unlock” restricting app access to encryption keys.

404 Media recently reported that law enforcement warned that securely stored iPhones awaiting forensic examination are mysteriously rebooting, making them harder to unlock.

Law enforcement warned that securely stored iPhones awaiting forensic examination are mysteriously rebooting, making them much harder to unlock, per a document obtained by 404 Media.

404 Media obtained the document from a mobile forensics source and verified it with another source.

The document notes that some iPhones in a forensics lab, including those in Airplane mode or a Faraday box, rebooted unexpectedly, losing their “After First Unlock” (AFU) state.

iPhones in an “After First Unlock” (AFU) can be accessed by law enforcement by using forensics tools like Cellebrite.

Once rebooted, the devices went into a Before First Unlock (BFU) state, which makes unlocking them much harder, as current tools can’t crack BFU iPhones. Three iPhones running iOS 18.0 were added to the lab on October 3, and officials hypothesize that these devices may have communicated with other iPhones in AFU mode, triggering a reboot if they were inactive or off-network. This could impact both evidence and personal devices running iOS 18.

This is the first time that this mysterious behaviour has been documented. The authors of the document appear to be law enforcement officials in Detroit. The experts believe a new security feature implemented in iOS 18 caused iPhones to reboot when disconnected from cellular networks.

“After being rebooted, iPhones are generally more secure against tools that aim to crack the password of and take data from the phone.” reported 404 Media.

“The purpose of this notice is to spread awareness of a situation involving iPhones, which is causing iPhone devices to reboot in a short amount of time (observations are possibly within 24 hours) when removed from a cellular network,” reads the document seen by 404 Media. 

The document recommends forensics labs to isolate AFU devices from iOS 18 devices to prevent unexpected reboots that erase the AFU state. It suggests taking inventory to check if any AFU devices have already rebooted.

404 Media now confirmed that Apple quietly introduced code into iOS 18.1 that reboots iPhones if it has not been unlocked for a period of time. The feature makes it harder for police forensics analysis of the devices.

“Apple indeed added a feature called ‘inactivity reboot’ in iOS 18.1.,” Dr.-Ing. Jiska Classen, a research group leader at the Hasso Plattner Institute, tweeted after 404 Media published on Thursday along with screenshots that they presented as the relevant pieces of code.” reported 404 Media.

“Apple indeed added a feature called “inactivity reboot” in iOS 18.1. This is implemented in keybagd and the AppleSEPKeyStore kernel extension. It seems to have nothing to do with phone/wireless network state. Keystore is used when unlocking the device.” Classen explained.

Apple has not yet disclosed details of the new security feature.

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Pierluigi Paganini

(SecurityAffairs – hacking, iPhones)