You'll now find a toggle switch labeled "USB Accessories" in the Touch ID & Passcode section of the Settings app labeled "USB Accessories".
Unlock iPhone to allow USB accessories to connect when it has been more than an hour since your iPhone was unlocked.
This chink in the USB Restricted Mode's armor can probably be closed, but it might prove annoying to users. The trick, then, is to attach a USB accessory to the port as soon as possible after stealing (or seizing) the iPhone, in order to stop it from locking down.
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. Notable in the new build is USB Restrictive Mode.
The research team isn't sure if third-party adaptors have a similar effect, but this same method can't be achieved with Apple's Lightning to 3.5mm adaptor.
Greyshift claimed it had already worked around that restriction but it might not have to, at least not for a while.
Aside from this, iOS 11.4.1 includes bug fixes for the Find My AirPods feature and syncing with Exchange accounts.
The iOS 11.4.1 upgrade is small by Apple standards - coming in at around 200MB - but it represents a big headache for the Federal Bureau of Investigation and other organizations that want to gain access to someone else's phone because it kills off the most common route to bypassing the device's security. Prior to iOS 11.4.1, isolating the iPhone inside a Faraday bag and connecting it to a battery pack would be enough to safely transport it to the lab. Law enforcement and private companies could leverage the loophole and design new hardware to continue to crack passcodes through the Lightning port.