NodeBB core doesn't have anything to prevent this. But plugins can be made to prevent multiple accounts from the same IP etc although it can be easily by passed.
Disallow user to quit a group
How can I prevent users from being able to quit a group ? Is there an option for it (that I have not found) or do I need to write a plugin (which hook to call ?) ?
No built in way to do this right now, although I think it would be useful as a core option in the group settings, like
Disable join requests. Can you open an issue on our tracker?
If you don't want to wait till it's implemented one hacky way to do it is to use the hook
'action:group.leave'and add the user back to the groups they just left.