CyberHunter
Local dataset, no network
// Other services

Port 3901: NIM Service Handler

Port 3901 is assigned by IANA to nimsh (NIM Service Handler).

3901

How nimsh works

Other services
client:3901nimshresponse client:3901nimshresponse

The client sends a request to port 3901 and the nimsh 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
Registered (1024-49151)
Category
Other services
01 Security

Is port 3901 dangerous?

We have no specific security note for port 3901. 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 3901

ServicePortTransportDescriptionReferenceUpdated
nimsh 3901 TCP, UDP NIM Service Handler - 2003-10

// source: IANA service name and port number registry

03 Check it

Which program uses port 3901, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3901'      # process listening on 3901
sudo lsof -nP -i :3901

macOS

sudo lsof -nP -i :3901

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3901 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3901
netstat -ano | findstr :3901

From another machine

nmap -p 3901 -sV <host>
sudo nmap -sU -p 3901 <host>
nc -zv <host> 3901

Block it in the firewall

sudo ufw deny 3901/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3901" -Direction Inbound -LocalPort 3901 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3901 used for?

Port 3901 is assigned by IANA to nimsh (NIM Service Handler).

Is port 3901 TCP or UDP?

Port 3901 is registered for TCP and UDP.

Is it safe to open port 3901?

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 3901 is open?

On Linux run "ss -ltnup 'sport = :3901'", on macOS "lsof -nP -i :3901", and on Windows "netstat -ano | findstr :3901" to see the local process. From another machine, "nmap -p 3901 <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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