Port 3389 MS-WBT-SERVER
Port 3389 is the IANA-assigned ms-wbt-server port for MS WBT Server (TCP / UDP).
What is port 3389 used for?
Port 3389 is assigned to ms-wbt-server and uses TCP / UDP. The IANA registry describes the service as “MS WBT Server”. It sits in the registered range, the block used by databases, application servers and developer tooling. Port conflicts here are common when several local services start at once.
Ports are the transport-layer address a service listens on. A client that wants to reach ms-wbt-server connects to port 3389. A TCP connection is refused when nothing is listening, while a UDP request simply goes unanswered. That is why a port conflict appears whenever two processes try to bind the same number.
Use the commands below to confirm whether port 3389 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.
Browse all Remote access ports
Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [Jordan_Marchese].
Check and block port 3389
Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.
Check on Linux
sudo ss -tlpn 'sport = :3389'
sudo ss -ulpn 'sport = :3389'Check on Windows
Get-NetTCPConnection -LocalPort 3389 -State Listen -ErrorAction SilentlyContinue
Get-NetUDPEndpoint -LocalPort 3389 -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 3389/tcp
sudo ufw deny 3389/udpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 3389 -j DROP
sudo iptables -A INPUT -p udp --dport 3389 -j DROPThese commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.
Is port 3389 safe to expose?
RDP is heavily brute-forced and a top ransomware entry point. Require a VPN or zero-trust gateway, MFA and network-level authentication. Treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
Where port 3389 is usually used
Most traffic on port 3389 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Administrators connecting through a bastion host or VPN to manage a machine.
- Automation and CI jobs opening short-lived sessions to run commands.
- Port forwarding that keeps an internal service off the public network.
Probe the RDP listener
RDP should sit behind a VPN or zero-trust gateway. This probe only checks reachability.
nc -vz 10.0.0.25 3389Common problems with port 3389
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 3389. A timeout more often means a firewall drop, a wrong host or a service bound to a different interface.
Port already in use
Find the process holding the port with sudo ss -tlpn 'sport = :3389' or sudo lsof -i :3389. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.
Firewall rule did not survive a reboot
UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.
The port is blocked but still reachable
A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.
Port 3389 at a glance
| Port number | 3389 |
|---|---|
| Service name | ms-wbt-server |
| Transport protocol | TCP / UDP |
| Category | Remote access |
| Range | Registered port (1024–10000) |
| Risk level | High |
| Registered assignee | [Jordan_Marchese] |
| Registry description | MS WBT Server |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 3389 used for?
Port 3389 (MS-WBT-SERVER) uses TCP / UDP. MS WBT Server.
How do I check if port 3389 is open?
On Linux run `sudo ss -tlpn 'sport = :3389'` and `sudo ss -ulpn 'sport = :3389'`. On Windows run `Get-NetTCPConnection -LocalPort 3389 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 3389 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 3389; empty output usually means nothing is bound to it.
How do I block port 3389?
With UFW run `sudo ufw deny 3389/tcp` and `sudo ufw deny 3389/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 3389 -j DROP` and `sudo iptables -A INPUT -p udp --dport 3389 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 3389 safe to expose?
RDP is heavily brute-forced and a top ransomware entry point. Require a VPN or zero-trust gateway, MFA and network-level authentication. Nevertheless, treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
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Primary data: IANA Service Name and Transport Protocol Port Number Registry.
Last reviewed 2026-10-30 · Methodology · About · Privacy