There are several ways, but they are all quite involved. Reading the comments Helix’s comment seems the easiest, given that VirtualBox can really use raw disks, which I have not heard of before. To this I wish to add, if this method works you don’t need to worry about drivers. The linux kernel has all the drivers you are likely to need & initrd is taken care of by all the distro installers, so you just need to directly install from the iso normally & not use an automated installers if VirtualBox has such options. I don’t have USB drives and they cost too much for something i never use. If you care about Linux it’s worth getting a usb drive, $4 gets you a usable drive in most parts of the world. (8GB is enough)