You don’t need to give the VM network access to download the software if you have a linux host. You can directly mount a virtual box drive from the host, copy the file(s) onto the drive and then unmount it and start the VM as per normal.
Search for qemu-nbd iirc (network block device) - I have the how to details saved on my host (ie not on me) so ping me if you want them. Note it’s a qemu app that works for vbox
I have considerably more characters than 6 at lloyds