At
http://libvirt.org/drvvbox.html it says:
"The libvirt VirtualBox driver can manage any VirtualBox version from version
2.2 onwards"
However it looks like 4.2 is yet implemented. Perhaps the page could be
updated?
Thanks,
Brian Candler.
P.S. I see work is ongoing in this area:
http://www.redhat.com/archives/libvir-list/2012-October/msg00038.html
http://www.redhat.com/archives/libvir-list/2012-November/msg00575.html