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// IoT & industrial (ICS)

Port 5683: Constrained Application Protocol (CoAP)

Port 5683 is assigned by IANA to coap (Constrained Application Protocol (CoAP)).

5683

How coap works

IoT & industrial (ICS)
controllerPLCcoapno authentication controllerPLCcoapno authentication

A controller sends commands to an industrial device on port 5683, which acts on the physical process.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
IoT & industrial (ICS)
01 Security

Is port 5683 dangerous?

We have no specific security note for port 5683. 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 5683

ServicePortTransportDescriptionReferenceUpdated
coap 5683 TCP, UDP Constrained Application Protocol (CoAP) RFC 8323 2017-12-22

// source: IANA service name and port number registry

03 Check it

Which program uses port 5683, and is it reachable?

Linux

sudo ss -ltnup 'sport = :5683'      # process listening on 5683
sudo lsof -nP -i :5683

macOS

sudo lsof -nP -i :5683

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 5683 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 5683
netstat -ano | findstr :5683

From another machine

nmap -p 5683 -sV <host>
sudo nmap -sU -p 5683 <host>
nc -zv <host> 5683

Block it in the firewall

sudo ufw deny 5683/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 5683" -Direction Inbound -LocalPort 5683 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 5683 used for?

Port 5683 is assigned by IANA to coap (Constrained Application Protocol (CoAP)).

Is port 5683 TCP or UDP?

Port 5683 is registered for TCP and UDP.

Is it safe to open port 5683?

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 5683 is open?

On Linux run "ss -ltnup 'sport = :5683'", on macOS "lsof -nP -i :5683", and on Windows "netstat -ano | findstr :5683" to see the local process. From another machine, "nmap -p 5683 <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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