Apple quietly introduced code into iOS 18.1 which reboots the device if it has not been unlocked for a period of time, reverting it to a state which improves the security of iPhones overall and is making it harder for police to break into the devices, according to multiple iPhone security experts.
On Thursday, 404 Media reported that law enforcement officials were freaking out that iPhones which had been stored for examination were mysteriously rebooting themselves. At the time the cause was unclear, with the officials only able to speculate why they were being locked out of the devices. Now a day later, the potential reason why is coming into view.
“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.
It’s more complicated than that. It’s called USB restricted mode. The lightning port is always willing to do a minimal subset of the protocols that it supports in order to do smart charging. By default most of the protocols it supports are disabled in BFU state. In AFU state it gets more complex than that. Accessories that you’ve previously connected can connect for one hour after the device is locked. This helps keep USB restricted mode from being really annoying if you briefly disconnect and reconnect an accessory.
USB restricted mode can be disabled by a user option (Settings > [Touch / Face] ID & Passcode > Allow Access When Locked > Accessories) or by a configuration profile. Disabling it allows accessories to connect at any time, and generally lowers the security of your device. But in some cases that’s necessary, for instance when you use an accessibility accessory to use your device.
If USB restricted mode is a concern for you, you should consider Lockdown Mode (Settings > Privacy & Security > Lockdown Mode). This changes several settings on your device to make it much more resilient to attack.
Very informative. Thank you.
You mentioned the lightning port. Is there any difference with the newer phones with USB-C when it comes to these functions?
I’m glad you find this informative. It’s a topic that’s important to me both personally and professionally, and there’s a lot of wrong information out there. But the best and most reliable info is in the Apple Platform Security Guide, such as Activating data connections securely and Direct memory access protections for Mac computers.
In this topic I don’t think there’s any important difference between USB-C and lightning. Both form factors support a bunch of USB protocols as well as some Apple-only protocols, and both have USB restricted mode.