Sigh.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=733940
FWIW, if you install the ntp package and do ntpdc -n -c monlist localhost you'll get a response but I haven't checked if it's configured by default to reject non-LAN requests.
FWIW, if you install the ntp package and do ntpdc -n -c monlist localhost you'll get a response but I haven't checked if it's configured by default to reject non-LAN requests.
Before installing ntp (from another host on my LAN):
$ ntpdc -n -c monlist 192.168.1.50
ntpdc: read: Connection refused
$ ntpdc -n -c monlist 192.168.1.50
192.168.1.50: timed out, nothing received
***Request timed out
$ ntpdc -n -c monlist localhost
remote address port local address count m ver rstr avgint lstint
===============================================================================
91.189.94.4 123 192.168.1.50 1 4 4 1d0 54 54
...Being able tod this via localhost is not a problem, it's when it's open to the internet.