UPDATE: Please see https://macmule.com/2017/11/30/imaroot-its-fixed-somethings-broken-fixed-that-now-too/
Earlier tonight I was pointed to a tweet that seemed to show an easy manner for people on High Sierra were able to simply enable root.
Well, the vuln is real. See below for a link to a fix for the issue whilst we await Apple to push a High Sierra update.