I have Xubuntu 18.04 VirtualBox Wersja 5.2.18_Ubuntu r123745 and Oracle VM VirtualBoxExtension Pack. I installed Windows 10 and it works OK. I marked insetting for two way communication with base system and two way dragand drop. I marked base system home folder to by seen by Windows 10.
Windows 10 do notsee any of the folders on base system, not see USB, drag and dropdoes not work. Also controller USB is grey and mark as USB 1.1.

How to solve it.Extension Pack is mark as green, installed.