Vulcan/packages/vulcan-comments/lib/permissions.js

import Users from 'meteor/vulcan:users';

const guestsActions = [
  "comments.view"
];
Users.groups.guests.can(guestsActions);

const membersActions = [
  "comments.view",
  "comments.new", 
  "comments.edit.own", 
  "comments.remove.own", 
  "comments.upvote", 
  "comments.cancelUpvote", 
  "comments.downvote",
  "comments.cancelDownvote"
];
Users.groups.members.can(membersActions);

const adminActions = [
  "comments.edit.all",
  "comments.remove.all"
];
Users.groups.admins.can(adminActions);