I have UbuntuMATE 16.04 and recently installed Windows XP on VirtualBox, but everytime y connect a USB stick or my External Hard Drive it's not recognized by Windows.
Ubuntu recognizes both USB stick and the External Hard Drive. I'm running the latest version of VirtualBox.
I had this same issue, and even though my account is sudo, I still needed to do this to get access to my USB on the client machine.
sudo usermod -a -G vboxusers your_user_name
That will hopefully fix the issue.
In addition to installing GuestAdditions, make sure you have Service Pack 3 for XP. In spite of all of that, XP may not have installed the USB drivers (it's always been notorious for doing so).
In the Windows guest OS, go to Control Panel > System > Hardware and see if you have yellow question marks on your USB inerface(s). If so, try right-clicking and select "Install Drivers."
If you open the settings for the OS and go under the USB tab there is a little USB stick with a plus symbol. Click this and select your USB stick.
