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// IoT & industrial (ICS)

Port 802: Modbus Application Protocol Secure

Port 802 is assigned by IANA to mbap-s (Modbus Application Protocol Secure).

802

How mbap-s works

IoT & industrial (ICS)
controllerPLCmbap-sno authentication controllerPLCmbap-sno authentication

A controller sends commands to an industrial device on port 802, 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
Well-known (0-1023)
Category
IoT & industrial (ICS)
01 Security

Is port 802 dangerous?

We have no specific security note for port 802. 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 802

ServicePortTransportDescriptionReferenceUpdated
mbap-s 802 TCP, UDP Modbus Application Protocol Secure - 2014-06-10

// source: IANA service name and port number registry

03 Check it

Which program uses port 802, and is it reachable?

Linux

sudo ss -ltnup 'sport = :802'      # process listening on 802
sudo lsof -nP -i :802

macOS

sudo lsof -nP -i :802

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 802 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 802
netstat -ano | findstr :802

From another machine

nmap -p 802 -sV <host>
sudo nmap -sU -p 802 <host>
nc -zv <host> 802

Block it in the firewall

sudo ufw deny 802/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 802" -Direction Inbound -LocalPort 802 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 802 used for?

Port 802 is assigned by IANA to mbap-s (Modbus Application Protocol Secure).

Is port 802 TCP or UDP?

Port 802 is registered for TCP and UDP.

Is it safe to open port 802?

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 802 is open?

On Linux run "ss -ltnup 'sport = :802'", on macOS "lsof -nP -i :802", and on Windows "netstat -ano | findstr :802" to see the local process. From another machine, "nmap -p 802 <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 :2221 EtherNet/IP over TLS tcp · udp

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