Chrome OS will block the USB ports on locked Chromebooks
 

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 Chro...

https://www.engadget.com/2019/01/02/...ocked-devices/