Comment 4 for bug 1767453

The bug appeared while upgrading from Ubuntu 16 to Ubuntu 18. It is a very serious bug, since many other packages depend on ca-certificates and were left unconfigured. Lots of error messages in the screen.
When the upgrade finished, the system was left in a very bad situation with so many non-configured packages. No workable reboot-shutdown button, not functioning menus ... If moving to a virtual terminal (Alt-F1) the virtual console did not work either, so the configuration error of ca-certificates is a really serious bug.
I did not dare to perform a hard poweroff and poweron because I was not confident that the system was going to be able to boot at all.
Fortunately enough, right clicking in the screen worked and I was able to open a terminal. From that terminal, I keyed firefox (not accesible through non-working menus) and downloaded from ubuntu archive the version 20170717 of ca-certificates and install it replacing the buggy 20180409 using dpkg -i.
After this, I performed
dpkg --configure -a
and all not-fully installed packages got correctly configured.
I had to poweroff via the button (no other choice) and when powering on again, Ubuntu 18 appeared with no other issue so far.