Comment 8 for bug 1775672

Using ...

sudo apt install --reinstall virtualbox-dkms

... I have the same issue as user zwets above in this message thread:

whiptail command hangs infinitely and does not show a menu possibly because of the bad environment it is running in.

My workaround was to kill the perl process and run it standalone ...

sudo perl -w /usr/share/debconf/frontend /usr/sbin/update-secureboot-policy --enroll-key

... in a usual interactive shell, so that whiptail shows the menu to set a password.

Afterwards (that is, after reboot and enrolling this password key during boot) VirtualBox is running for me on Ubuntu 18.04 with secure boot and does not complain about an unsigned vboxdrv anymore.

Seems to be a design flaw to prevent interactivity during installation.