NAT network needs to be the first adapter in VM settings.
List vms:
VBoxManage list vms
Create rule:
VBoxManage modifyvm "Debian 9" --natpf1 "debian9ssh,tcp,,<hostport i.e. 5622>,,<guest port i.e. 22>"
Show port forward:
VBoxManage showvminfo "Debian 9" | grep Rule
Connect:
ssh -p 5622 root@127.0.0.1