Since the beginning that I knew virtualbox, I wonder how this engine access to my usb stick directly without moving the content to the host first. Actually there is a way how we can do that.
First, add the user to vboxusers group. Use kuser or nano /etc/group in the terminal.
Now open the virtualbox, click usb in the setting area. But don’t run the virtual machine yet. Set the necessary setting in the usb dialog box, then save.
Now start the virtual machine, you will find the usb in the drive section.
I do this to windows virtual machine.