The toggle is off by default, which means that once your iOS device has been locked for more than an hour, the operating system will no longer allow USB access to connect to the device.
Apple released iOS 11.4.1, tvOS 11.4.1, and watchOS 4.3.2 today with minor bug fixes for its iPhones, iPads, HomePods, Apple TVs, and Apple Watches, but there was one surprise in the software: USB Restricted Mode, a feature created to block iPhone-cracking USB devices used by law enforcement agencies, has finally arrived.
The new feature will not prevent the phone from being charged, but if you want to unlock or transfer any data to or from the device, you will need to enter the phone's passcode on the touchscreen. It also doesn't work if USB Restricted Mode has already been triggered (past the one-hour mark). However, if you want the update right away, you can use the Home app on your iPhone to do so.
However, security firm Elcomsoft noted in a blog post that you can reset this one-hour timer by plugging in a USB accessory - like this Lightning to USB 3 Camera Adapter that Apple itself makes - before the feature kicks in, so as to buy time to transport the phone back to a secure facility for investigation. The resetting of the built-in feature works even with an untrusted USB accessory, one that has never been paired with the device before. Importantly, this only helps if the iPhone has still not entered USB Restricted Mode.
While Apple might fix the flaw in the next iOS 11.4 release or in the iOS 12, Afonin doesn't consider it as a severe vulnerability and calls it an "oversight".
Security researchers at ElcomSoft discovered the security hole, which can be found in iOS 11.4.1. What's new in tvOS 11.4.1 This update includes general performance and stability improvements. Law enforcement and private companies could leverage the loophole and design new hardware to continue to crack passcodes through the Lightning port.