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// IoT & industrial (ICS)

Port 4843: OPC UA TCP Protocol over TLS/SSL

Port 4843 is assigned by IANA to opcua-tls (OPC UA TCP Protocol over TLS/SSL).

4843

How opcua-tls works

IoT & industrial (ICS)
controllerPLCopcua-tlsno authentication controllerPLCopcua-tlsno authentication

A controller sends commands to an industrial device on port 4843, 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 4843 dangerous?

We have no specific security note for port 4843. 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 4843

ServicePortTransportDescriptionReferenceUpdated
opcua-tls 4843 TCP, UDP OPC UA TCP Protocol over TLS/SSL - 2017-05-23

// source: IANA service name and port number registry

03 Check it

Which program uses port 4843, and is it reachable?

Linux

sudo ss -ltnup 'sport = :4843'      # process listening on 4843
sudo lsof -nP -i :4843

macOS

sudo lsof -nP -i :4843

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4843 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 4843
netstat -ano | findstr :4843

From another machine

nmap -p 4843 -sV <host>
sudo nmap -sU -p 4843 <host>
nc -zv <host> 4843

Block it in the firewall

sudo ufw deny 4843/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 4843" -Direction Inbound -LocalPort 4843 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 4843 used for?

Port 4843 is assigned by IANA to opcua-tls (OPC UA TCP Protocol over TLS/SSL).

Is port 4843 TCP or UDP?

Port 4843 is registered for TCP and UDP.

Is it safe to open port 4843?

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 4843 is open?

On Linux run "ss -ltnup 'sport = :4843'", on macOS "lsof -nP -i :4843", and on Windows "netstat -ano | findstr :4843" to see the local process. From another machine, "nmap -p 4843 <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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