I gave the editors such permissions:
auth | user | can add/change user - ON
auth | permissions | can add/change permissions - OFF
Still, when editing, they can change their permissions (and allow themselves actions they shouldn't do). I've found a ticket from 2yrs ago: http://code.djangoproject.com/ticket/6519 and it still works this way.
How to allow user edition (email, passwords, etc..) but block permissions change?