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// Remote access

Port 6000: X Window System

Port 6000 is assigned by IANA to x11 (X Window System).

6000

How x11 works

Remote access
terminal:6000x11 terminal:6000x11

The client opens a session to port 6000: each command typed is sent to the server, which runs it and returns the output.

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
Remote access
01 Security

Is port 6000 dangerous?

We have no specific security note for port 6000. Its risk depends on the program actually listening on it. General advice for remote access services:

  • Do not expose remote administration directly: use a VPN or a zero-trust access proxy.
  • Require MFA or key-based authentication and lock out brute-force attempts.
  • Log every login and alert on new source addresses.
02 Registry

IANA registry entries for port 6000

ServicePortTransportDescriptionReferenceUpdated
x11 6000-6063 TCP, UDP X Window System
Reported: Known Unauthorized Use on port 6003
 - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 6000, and is it reachable?

Linux

sudo ss -ltnup 'sport = :6000'      # process listening on 6000
sudo lsof -nP -i :6000

macOS

sudo lsof -nP -i :6000

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 6000 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 6000
netstat -ano | findstr :6000

From another machine

nmap -p 6000 -sV <host>
sudo nmap -sU -p 6000 <host>
nc -zv <host> 6000

Block it in the firewall

sudo ufw deny 6000/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 6000" -Direction Inbound -LocalPort 6000 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 6000 used for?

Port 6000 is assigned by IANA to x11 (X Window System).

Is port 6000 TCP or UDP?

Port 6000 is registered for TCP and UDP.

Is it safe to open port 6000?

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. Do not expose remote administration directly: use a VPN or a zero-trust access proxy.

How do I check if port 6000 is open?

On Linux run "ss -ltnup 'sport = :6000'", on macOS "lsof -nP -i :6000", and on Windows "netstat -ano | findstr :6000" to see the local process. From another machine, "nmap -p 6000 <host>" shows whether it is reachable.

05 Related
:22 SSH tcp · udp · sctp · moderate risk :3389 RDP tcp · udp · critical risk :23 Telnet tcp · udp · critical risk :5900 VNC tcp · udp · critical risk :5985 WinRM (HTTP) tcp · udp · high risk :5986 WinRM (HTTPS) tcp · udp · high risk :10000 Webmin tcp · udp · high risk :89 SU/MIT Telnet Gateway tcp · udp

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