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// IoT & industrial (ICS)

Port 5684: Constrained Application Protocol (CoAP)

Port 5684 is assigned by IANA to coaps (Constrained Application Protocol (CoAP)).

5684

How coaps works

IoT & industrial (ICS)
controllerPLCcoapsno authentication controllerPLCcoapsno authentication

A controller sends commands to an industrial device on port 5684, which acts on the physical process. Everything is encrypted: someone on the path only sees unreadable bytes.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
EncryptedTLS or built-in crypto
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
IoT & industrial (ICS)
01 Security

Is port 5684 dangerous?

We have no specific security note for port 5684. Its risk depends on the program actually listening on it. General advice for iot & industrial (ics) services:

  • Industrial and IoT protocols often have no authentication: never expose them to the Internet.
  • Segment OT networks from IT and use protocol-aware firewalls.
  • Monitor with an ICS-aware intrusion detection system.
02 Registry

IANA registry entries for port 5684

ServicePortTransportDescriptionReferenceUpdated
coaps 5684 TCP, UDP Constrained Application Protocol (CoAP) RFC 7301, RFC 8323 2017-12-22

// source: IANA service name and port number registry

03 Check it

Which program uses port 5684, and is it reachable?

Linux

sudo ss -ltnup 'sport = :5684'      # process listening on 5684
sudo lsof -nP -i :5684

macOS

sudo lsof -nP -i :5684

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 5684 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 5684
netstat -ano | findstr :5684

From another machine

nmap -p 5684 -sV <host>
sudo nmap -sU -p 5684 <host>
nc -zv <host> 5684

Block it in the firewall

sudo ufw deny 5684/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 5684" -Direction Inbound -LocalPort 5684 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 5684 used for?

Port 5684 is assigned by IANA to coaps (Constrained Application Protocol (CoAP)).

Is port 5684 TCP or UDP?

Port 5684 is registered for TCP and UDP.

Is it safe to open port 5684?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Industrial and IoT protocols often have no authentication: never expose them to the Internet.

How do I check if port 5684 is open?

On Linux run "ss -ltnup 'sport = :5684'", on macOS "lsof -nP -i :5684", and on Windows "netstat -ano | findstr :5684" to see the local process. From another machine, "nmap -p 5684 <host>" shows whether it is reachable.

05 Related
:1883 MQTT tcp · udp · high risk :8883 MQTT over TLS tcp · udp · moderate risk :502 Modbus TCP tcp · udp · critical risk :102 Siemens S7 (ISO-TSAP) tcp · udp · critical risk :47808 BACnet udp · tcp · critical risk :20000 DNP3 tcp · udp · sctp · critical risk :44818 EtherNet/IP tcp · udp · critical risk :802 Modbus Application Protocol Secure tcp · udp

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