Via OSS-sec:


Hm, if this warrants a CVE for lightdm, then gdm3 needs one also:

 https://bugzilla.gnome.org/show_bug.cgi?id=704284
 http://bugs.debian.org/683338

Basically, when gdm3 is configured to not show a list of users (but
instead shows a blank box for the login prompt), if the user clicks
"cancel" or hits the escape key, then the greeter gets put into a mode
without any way to log in (no prompts available).

I've tried to debug it but it appears to be due to some sort of
timing-dependent case.  When i step through the code with gdb, i haven't
been able to reproduce the issue.

It is definitely a bad situation for machines in public locations with
this configuration.