I've played in many CTFs and written challenges for a few. Unpleasant surprises in the binaries, especially when run as root aren't uncommon.

You could also attack the VM:

http://www.cvedetails.com/vulnerability-list/vendor_id-93/pr...

Given this, what is the best first step? Best we can tell, he was running root in a VM that was running as an ordinary user. What more can be done, aside from running it on a throwaway machine? Running on a cloud instance, perhaps?

Perhaps a LiveCD/LiveUSB, with a VM inside of it?

Then a compromise would need to be:

Local VM user -> root VM user -> local LiveCD user -> root liveCD user -> hardware exploits

Christ I had no idea Virtualbox was that riddled with holes. I wonder how many of those have been fixed.