CyberHunter
Local dataset, no network
// Other services

Port 18: Message Send Protocol (historic)

Port 18 is assigned by IANA to msp (Message Send Protocol (historic)).

18

How msp works

Other services
client:18mspresponse client:18mspresponse

The client sends a request to port 18 and the msp service answers.

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
Other services
01 Security

Is port 18 dangerous?

We have no specific security note for port 18. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 18

ServicePortTransportDescriptionReferenceUpdated
msp 18 TCP, UDP Message Send Protocol (historic) - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 18, and is it reachable?

Linux

sudo ss -ltnup 'sport = :18'      # process listening on 18
sudo lsof -nP -i :18

macOS

sudo lsof -nP -i :18

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 18 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 18
netstat -ano | findstr :18

From another machine

nmap -p 18 -sV <host>
sudo nmap -sU -p 18 <host>
nc -zv <host> 18

Block it in the firewall

sudo ufw deny 18/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 18" -Direction Inbound -LocalPort 18 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 18 used for?

Port 18 is assigned by IANA to msp (Message Send Protocol (historic)).

Is port 18 TCP or UDP?

Port 18 is registered for TCP and UDP.

Is it safe to open port 18?

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. Close the port if nothing on the host needs it.

How do I check if port 18 is open?

On Linux run "ss -ltnup 'sport = :18'", on macOS "lsof -nP -i :18", and on Windows "netstat -ano | findstr :18" to see the local process. From another machine, "nmap -p 18 <host>" shows whether it is reachable.

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