Finally gave up and set iptables rules.
/sbin/iptables -A INPUT -p tcp -s 127.0.0.1 --dport 4000 -j ACCEPT
/sbin/iptables -A INPUT -p tcp --dport 4000 -j DROP
Not a fan of doing it that way, since it's easy to forget something set elsewhere.
Network app developers: Listening on 0.0.0.0 by default without telling the admin how to easily change it is a FRIKKING BAD IDEA!!!
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