iPhone USB Restricted Mode is Here

USB Restricted Mode is enabled by default once you install iOS 11.4.1. USB Restricted mode makes it more difficult for someone to brute-force their way into your device or make use of any other clever exploit, deployed via an iPhone or iPad’s Lightning port, to get past your device’s passcode.

USB Restricted Mode is designed to shut off access to data on an iPhone or iPad when new USB accessories are plugged into the Lightning port, as long as it's been more than an hour since you last unlocked your iPhone. The feature prevents people from using gadgets such as the GrayKey tool from accessing the phone's information.

The Russian computer security company Elcomsoft notes: "What we discovered is that iOS will reset the USB Restrictive Mode countdown timer even if one connects the iPhone to an untrusted USB accessory, one that has never been paired to the iPhone before (well, in fact the accessories do not require pairing at all). In other words, once the police officer seizes an iPhone, he or she would need to immediately connect that iPhone to a compatible USB accessory to prevent USB Restricted Mode lock after one hour. Importantly, this only helps if the iPhone has still not entered USB Restricted Mode."

So if someone who wanted access to the data on your phone, be they law enforcement officers or hackers, obtained your device within the hour, they could keep access open by continuously plugging in an accessory and resetting the clock.

In the settings menu under 'Touch ID & Passcode' scroll down and to the 'Allow Access When Locked" menu and be sure that USB Accessories is NOT highlighted (as shown above). You do not want USB Accessories to access your iPhone when it is locked.

As noted by Elcomsoft, if someone can plug a USB device into your phone before it goes into restricted mode, it will be possible to keep resetting the one hour timer. And, of course, if someone gets your passcode he or she could just access your phone and disable the USB Restricted mode.

If you think you might be in a position where an adversary could gain physical control of your phone - turn it off. iPhone requires your passphrase after restarting.