virtualbox.org

Dear Sir,

I use WindowServer 2012 Foundation Edition as Host OS.
Do I need Remote Desktop Service license of the WindowServer 2012 to use VirtualBox?

Please advice.

Nobody can answer this kind of question except the license provider, which is Microsoft in this case.
Anything that anyone can say here will protect you from a valid licensing.

Now, with some advice words, if you only want to access the server yourself via RDP, no you don't need extra licensing. If you want to turn your server into a remote desktop server (more than 2 connections AFAIK), yes you'll need an extra license.
But regardless, it has nothing to do with Virtualbox. Think of your VM as another regular physical machine.

Thank you very much