CyberHunter
Local dataset, no network
// Other services

Port 3933: PL/B App Server User Port

Port 3933 is assigned by IANA to plbserve-port (PL/B App Server User Port).

3933

How plbserve-port works

Other services
client:3933plbserve-portresponse client:3933plbserve-portresponse

The client sends a request to port 3933 and the plbserve-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 3933 dangerous?

We have no specific security note for port 3933. 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 3933

ServicePortTransportDescriptionReferenceUpdated
plbserve-port 3933 TCP, UDP PL/B App Server User Port - 2003-11

// source: IANA service name and port number registry

03 Check it

Which program uses port 3933, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3933'      # process listening on 3933
sudo lsof -nP -i :3933

macOS

sudo lsof -nP -i :3933

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3933 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3933
netstat -ano | findstr :3933

From another machine

nmap -p 3933 -sV <host>
sudo nmap -sU -p 3933 <host>
nc -zv <host> 3933

Block it in the firewall

sudo ufw deny 3933/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3933" -Direction Inbound -LocalPort 3933 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3933 used for?

Port 3933 is assigned by IANA to plbserve-port (PL/B App Server User Port).

Is port 3933 TCP or UDP?

Port 3933 is registered for TCP and UDP.

Is it safe to open port 3933?

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 3933 is open?

On Linux run "ss -ltnup 'sport = :3933'", on macOS "lsof -nP -i :3933", and on Windows "netstat -ano | findstr :3933" to see the local process. From another machine, "nmap -p 3933 <host>" shows whether it is reachable.

05 Related
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