Port 4369 EPMD · TCP

What runs on port 4369

EPMD (Erlang Port Mapper Daemon): tells Erlang nodes which dynamic port other nodes are listening on. RabbitMQ, CouchDB, ejabberd and anything built on Erlang/OTP run it. Exposed, it reveals node names and, with the Erlang cookie, gives full remote code execution, which is a frequently exploited misconfiguration.

Software that uses it: RabbitMQ · CouchDB · ejabberd · Riak · any Erlang/Elixir cluster

Should port 4369 be open?

Private network or VPN only. Nothing good comes from this port being reachable from the internet. Keep it on an internal network, reach it over a VPN or an SSH tunnel, and firewall it from everything that does not need it.

• epmd -names lists the nodes; if that works from outside the cluster network, close the port.
• Set inet_dist_listen_min/max to a fixed range and firewall both it and 4369.

Check port 4369

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :4369'
sudo lsof -i :4369

# from another machine: is it reachable?
nc -zv host 4369
nmap -p 4369 host
curl -v telnet://host:4369      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 4369

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 4369 proto tcp
sudo ufw deny 4369/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 4369 accept
nft add rule inet filter input tcp dport 4369 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 4369 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 4369 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=4369 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 4369" with no source is just "open".

Related ports

• 5672 AMQP — RabbitMQ
• 15672 RabbitMQ management
• 25672 RabbitMQ inter-node

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions