Even when your Chromebook is locked, bad actors can access it using a "Rubber Ducky," or malicious USB drive that mimics a keyboard. Chrome OS will soon put a stop to those attacks with a feature called USBGuard, seen in a Canary Chrome build by Chrome Story. It stops the operating system from reading code or executing commands from USB devices when your Chromebook is locked. The feature is similar to what Apple introduced in a recent build of IOS 11 that stops USB activity if a device has been locked for more than an hour.
Via: ZDNet
Source: Chromium