CyberHunter
Local dataset, no network
// Other services

Port 501: STMF

Port 501 is assigned by IANA to stmf (STMF).

501

How stmf works

Other services
client:501stmfresponse client:501stmfresponse

The client sends a request to port 501 and the stmf 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 501 dangerous?

We have no specific security note for port 501. 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 501

ServicePortTransportDescriptionReferenceUpdated
stmf 501 TCP, UDP STMF - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 501, and is it reachable?

Linux

sudo ss -ltnup 'sport = :501'      # process listening on 501
sudo lsof -nP -i :501

macOS

sudo lsof -nP -i :501

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 501 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 501
netstat -ano | findstr :501

From another machine

nmap -p 501 -sV <host>
sudo nmap -sU -p 501 <host>
nc -zv <host> 501

Block it in the firewall

sudo ufw deny 501/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 501" -Direction Inbound -LocalPort 501 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 501 used for?

Port 501 is assigned by IANA to stmf (STMF).

Is port 501 TCP or UDP?

Port 501 is registered for TCP and UDP.

Is it safe to open port 501?

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 501 is open?

On Linux run "ss -ltnup 'sport = :501'", on macOS "lsof -nP -i :501", and on Windows "netstat -ano | findstr :501" to see the local process. From another machine, "nmap -p 501 <host>" shows whether it is reachable.

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