This is very normal in 'nix' systems. '' indicates a locked account. (I've given up figuring out how to escape an asterisk)

ex:

  daemon:*:1:1::0:0:Owner of many system processes:/root:/usr/sbin/nologin
  operator:*:2:5::0:0:System &:/:/usr/sbin/nologin
  bin:*:3:7::0:0:Binaries Commands and Source:/:/usr/sbin/nologin
  tty:*:4:65533::0:0:Tty Sandbox:/:/usr/sbin/nologin

If the OS is letting you in with a '*'in the encrypted password field, something is very very wrong.

Only High Sierra is affected.

When you do this you'll get the creationTime and passwordLastSetTime as seconds since the 'epoch' – January 1, 1970, 00:00:00 (UTC). These are numbers like 1474441704.265237 which aren't very easy for a human to read :-)

To convert this into a human-readable date and time, open a terminal and do this:

  python

  >>> import time

  >>> time.strftime("%a, %d %b %Y %H:%M:%S", time.localtime(1474441704.265237))

You'll get something like 'Wed, 21 Sep 2016 07:08:24'

(I'm sure you can do this in other languages than python...)

One of my Macs is showing a root password change date of Nov 10th 2017. I can't explain that, so I'm reinstalling now. It did have sshd enabled and remotely accessible, though I thought root login was prohibited.

If I understood correctly, this particular bug was only exploitable from the GUI and this machine hasn't been away from home, so it's likely this isn't related, but posting here, in case it's part of a bigger picture.