There was a sudo file placed in /etc/sudoers.d by a web application called "supermon". The filename is also "supermon" and the contents are:
# Cmnd alias added for Supermon 7+:
Cmnd_Alias ASTERISK = /usr/bin/top, /sbin/ifconfig, /bin/df, /usr/sbin/asterisk, \
/bin/systemctl...