CyberHunter
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// Other services

Port 3931: MSR Plugin Port

Port 3931 is assigned by IANA to msr-plugin-port (MSR Plugin Port).

3931

How msr-plugin-port works

Other services
client:3931msr-plugin-portresponse client:3931msr-plugin-portresponse

The client sends a request to port 3931 and the msr-plugin-port 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 3931 dangerous?

We have no specific security note for port 3931. 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 3931

ServicePortTransportDescriptionReferenceUpdated
msr-plugin-port 3931 TCP, UDP MSR Plugin Port - 2003-11

// source: IANA service name and port number registry

03 Check it

Which program uses port 3931, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3931'      # process listening on 3931
sudo lsof -nP -i :3931

macOS

sudo lsof -nP -i :3931

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3931 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3931
netstat -ano | findstr :3931

From another machine

nmap -p 3931 -sV <host>
sudo nmap -sU -p 3931 <host>
nc -zv <host> 3931

Block it in the firewall

sudo ufw deny 3931/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3931" -Direction Inbound -LocalPort 3931 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3931 used for?

Port 3931 is assigned by IANA to msr-plugin-port (MSR Plugin Port).

Is port 3931 TCP or UDP?

Port 3931 is registered for TCP and UDP.

Is it safe to open port 3931?

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 3931 is open?

On Linux run "ss -ltnup 'sport = :3931'", on macOS "lsof -nP -i :3931", and on Windows "netstat -ano | findstr :3931" to see the local process. From another machine, "nmap -p 3931 <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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