The method, which bypasses the 10-entry attempt that erases an iOS device when the setting is enabled, allows a hacker to plug an iPhone or iPad into a computer and send all passcodes, from 0000 to 9999, all at once, triggering an input routine that takes priority over anything else on the device. Hickey demos the hack in the video below.
"Instead of sending passcodes one at a time and waiting, send them all in one go," he said.All that's required to use this brute force password cracking method is an iPhone or iPad that's turned on and locked and a Lightning cable, according to Hickey. It works on iOS devices up to iOS 11.3.
"If you send your brute-force attack in one long string of inputs, it'll process all of them, and bypass the erase data feature," he explained.
Hickey's iPhone cracking method takes between three and five seconds for each four-digit passcode, which means it's slow and not as advanced as other passcode cracking methods employed by companies like Grayshift, which makes the GrayKey box. For this method to guess a six-digit passcode, Hickey says it would take weeks.
Apple in iOS 12 is introducing a new USB Restricted Mode that may put a stop to the vulnerability that Hickey has discovered, as well as vulnerabilities exploited by tools like the GrayKey Box.
With USB Restricted Mode, enabled by default on iOS devices running iOS 12, USB access to an iPhone or iPad is cut off if it's been more than an hour since the device was last unlocked.
That means computers and other accessories can't be used to access a locked iPhone if it's been locked for over an hour, disabling access via a USB to Lightning cable.
Update: In a statement obtained by iMore, Apple says "the recent report about a passcode bypass on iPhone was in error, and a result of incorrect testing."