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July 11, 2018

Apple USB Restricted mode can be bypassed with a simple $39 accessory

by John_A

Julian Chokkattu/Digital Trends

It looks like Apple’s engineers may be going back to the drawing board, as it now seems the much lauded USB Restricted mode, created to thwart efforts to break into a locked iPhone, is able to be circumvented by a simple $39 accessory.

Introduced in iOS 11.4.1, USB Restricted mode kicks in automatically an hour after an iPhone was last unlocked, and disables all data connectivity of the Lightning port until the device is unlocked by a user, or by a trusted device. The mode was created to combat devices like the Graykey, which is used by law enforcement and other agencies to unlock iPhones. The introduction of USB Restricted mode means that these sorts of agencies now have an hour at most to unlock an iPhone, before it essentially becomes a chargeable brick. An hour isn’t a lot of time in law enforcement, and it was thought that this measure would effectively close Apple’s iPhone off entirely.

Apparently not. According to a series of tests by Elcomsoft Blog, while USB Restricted mode persists through restarts and software resets, and has so far proven invulnerable, the timer that engages Restricted mode can be paused by connecting a simple Lightning accessory. While the blog admits that tests are not yet complete, it seems that inserting Apple’s own Lightning to USB 3 Camera Adapter pauses the countdown, allowing agents the chance to unlock an iPhone through existing methods.

How does it work? If you imagine USB Restricted mode as a large and sturdy door, then inserting the camera adaptor essentially works as a doorstop, holding the door open. Because the accessory is otherwise engaging the Lightning port, USB Restricted mode apparently will not start the timer until the accessory has been removed.

However, like a doorstop, attaching the accessory after the hour has already passed does nothing to halt the process, just in the same way you can’t use a doorstop to open a locked door. What this basically means is that a seized iPhone simply has to be attached to an accessory, like the camera adaptor, in order to halt the hour timer on Restricted mode, effectively rendering Apple’s security pointless.

We have reached out to Apple for comment and will update if we hear back.

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