CyberHunter
Local dataset, no network
// Other services

Port 638: mcns-sec

Port 638 is assigned by IANA to mcns-sec (mcns-sec).

638

How mcns-sec works

Other services
client:638mcns-secresponse client:638mcns-secresponse

The client sends a request to port 638 and the mcns-sec 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 638 dangerous?

We have no specific security note for port 638. 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 638

ServicePortTransportDescriptionReferenceUpdated
mcns-sec 638 TCP, UDP mcns-sec - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 638, and is it reachable?

Linux

sudo ss -ltnup 'sport = :638'      # process listening on 638
sudo lsof -nP -i :638

macOS

sudo lsof -nP -i :638

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 638 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 638
netstat -ano | findstr :638

From another machine

nmap -p 638 -sV <host>
sudo nmap -sU -p 638 <host>
nc -zv <host> 638

Block it in the firewall

sudo ufw deny 638/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 638" -Direction Inbound -LocalPort 638 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 638 used for?

Port 638 is assigned by IANA to mcns-sec (mcns-sec).

Is port 638 TCP or UDP?

Port 638 is registered for TCP and UDP.

Is it safe to open port 638?

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 638 is open?

On Linux run "ss -ltnup 'sport = :638'", on macOS "lsof -nP -i :638", and on Windows "netstat -ano | findstr :638" to see the local process. From another machine, "nmap -p 638 <host>" shows whether it is reachable.

05 Related
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp

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