I got the latest extension pack installed, I got "USB2" activated in VB menu, and added a "new filter" there (for all detected USB's not some special).
Unfortunately Ubuntu still doesnt "permit" my guest OS to use the USB ports, so I ended up with the following terminal command, that I found:
sudo usermod -a -G vboxusers username
After that I was supposed to look up the USB-devices with:
vboxmanage list usbhost
but the list was empty.
Any idea what I can do? Most tutorials I found here were for older versions, so I dont know if they still up to date?