I happen to like virtualbox
I happen to like virtualbox, but I don't open up my VMs to 3rd parties. In cases where it _MIGHT_ happen, I can at least make sure root has a *strong* password/phrase.
I'll look into the 'paravirtualization' workaround anyway. Years ago I had trouble setting up thing like that, so new VMs aren't using "that", but since then it's probably working correctly so I'll re-visit.
In the mean time, vbox "NAT" lacks IPv6 support... so maybe "it's time" to look at another way to do networking.