Oleg Afonin of the desktop and mobile forensic tools maker Elcomsoft said in a blog post that the new feature was known as USB Restricted Mode and had been introduced in the beta version of the 11.4 release.
The claim comes in the wake of recent claims by the FBI that it had been unable to gain access to 7800 mobile devices in 2017, a claim that was questioned by US politicians. In 2016, the agency had a stoush with Apple over gaining access to an iPhone used by a terrorist to kill people in San Bernardino, California.
The FBI subsequently gained access to the iPhone through the services of a private firm known as Cellebrite. More recently, another company, GrayShift, has been reported to be selling devices to unlock the latest iPhones.
The functionality provided by this feature was that an iPhone or iPad would disable the USB data connection a week after the device had been last unlocked.
But some things were not still clear, Afonin added. "At this point, it is still unclear whether the USB port is blocked if the device has not been unlocked with a passcode for seven consecutive days; if the device has not been unlocked at all (password or biometrics); or if the device has not been unlocked or connected to a trusted USB device or computer.
"In our test, we were able to confirm the USB lock after the device had been left idle for seven days. During this period, we have not tried to unlock the device with Touch ID or connect it to a paired USB device. What we do know, however, is that after the seven days the Lightning port is only good for charging."
Afonin said this meant law enforcement would have to act within seven days to gain access to any data on an iPhone or iPad. "Apparently, iOS stores information about the date and time the device was last unlocked or had a data connection to a USB port," he said.
"After the seven days elapse, the Lightning port will be disabled. Once this happens, you will no longer be able to pair the device to a computer or USB accessory, or use an existing lockdown record, without unlocking the device with a passcode. The only thing you’ll be able to do is charging."
He said the arrival of USB Restricted Mode had been expected. "Companies such as Cellebrite and the recent newcomer GrayShift make their business by unlocking protected iPhones. While Cellebrite offers this exclusively as an in-house service, and the service is only available to select law enforcement agencies with proper court orders, GrayKey supplies the actual unlocking hardware to North American law enforcement.
"Both companies keep their lips shut as to the details of their techniques, so the exact method they use to gain access to the devices is not known to Apple. However, their ability to unlock even the latest hardware running the latest version of iOS is worrisome, so Apple is taking action with the USB Restricted Mode."