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// Other services

Port 3905: Mailbox Update (MUPDATE) protocol

Port 3905 is assigned by IANA to mupdate (Mailbox Update (MUPDATE) protocol).

3905

How mupdate works

Other services
client:3905mupdateresponse client:3905mupdateresponse

The client sends a request to port 3905 and the mupdate 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 3905 dangerous?

We have no specific security note for port 3905. 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 3905

ServicePortTransportDescriptionReferenceUpdated
mupdate 3905 TCP, UDP Mailbox Update (MUPDATE) protocol RFC 3656 -

// source: IANA service name and port number registry

03 Check it

Which program uses port 3905, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3905'      # process listening on 3905
sudo lsof -nP -i :3905

macOS

sudo lsof -nP -i :3905

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3905 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3905
netstat -ano | findstr :3905

From another machine

nmap -p 3905 -sV <host>
sudo nmap -sU -p 3905 <host>
nc -zv <host> 3905

Block it in the firewall

sudo ufw deny 3905/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3905" -Direction Inbound -LocalPort 3905 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3905 used for?

Port 3905 is assigned by IANA to mupdate (Mailbox Update (MUPDATE) protocol).

Is port 3905 TCP or UDP?

Port 3905 is registered for TCP and UDP.

Is it safe to open port 3905?

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 3905 is open?

On Linux run "ss -ltnup 'sport = :3905'", on macOS "lsof -nP -i :3905", and on Windows "netstat -ano | findstr :3905" to see the local process. From another machine, "nmap -p 3905 <host>" shows whether it is reachable.

05 Related
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