virtualbox-ose-kmod 6.1.18 (also previous version) built from ports without option VIMAGE. Kernel panic occurs when a virtual machine is started with a virtual network adapter in bridge mode (Settings -> Network -> "Attached to:" set to "Bridged Adapter").
Can you please provide a stacktrace or crash dump?
Created attachment 224149 [details] core.txt.0
Can you please add warning to pkg-message about this issue or somewhere else? We were beaten by this too and it is really hard to find what is the problem. The panic and reboot is so instant that I cannot see the panic message at all and as the vboxheadless is started automatically from rc.conf at boot the machine(s) are paniced again and again until booted in to single user mode and vboxheadless is turned of in rc.conf. I tried to build VirtualBox with VIMAGE just to make some change to test and it works again. But without VIMAGE it instantly panic the host on VM guest start.
For what it's worth, I just got bitten by this same issue. FreeBSD bogodyn.org 12.2-STABLE FreeBSD 12.2-STABLE stable/12-n233832-ebb3327d09c GENERIC amd64 virtualbox-ose-kmod-6.1.26 I had previously had the 5.x (-legacy) version installed and "upgraded" to 6.1.26. I had apparently tried to install this before when VIMAGE was default "off" and the ports system had that config stored. As a result, my system crashed hard the second I started virtualbox (I had not even started a VM --- it crashed on launching the gui). Rebuilding the kmod with VIMAGE on fixed the problem. It runs fine so long as VIMAGE is on. If VIMAGE must be on, it should no longer be an option in the port. At the very least there should alarm bells going off if the user tries to build without VIMAGE on. VIMAGE does default on now, but this doesn't help you if you have old configs and aren't prompted to change them.
*** This bug has been marked as a duplicate of bug 220003 ***