Port 135: MS-RPC
Port 135 is the Microsoft RPC endpoint mapper. Windows services use it to negotiate dynamic ports, which is why it is a frequent firewall and hardening target.
| Port number | 135 |
|---|---|
| Service | Microsoft RPC endpoint mapper |
| Protocol | TCP |
| Category | Windows |
| Default encryption | No |
How do I check whether port 135 is open?
Port 135 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 135 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 135 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':135 ' | Lists the process bound to port 135 on Linux. On macOS use lsof -nP -iTCP:135 -sTCP:LISTEN, on Windows netstat -ano | findstr :135 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 135 used for?
Port 135 is the Microsoft RPC endpoint mapper. Windows services use it to negotiate dynamic ports, which is why it is a frequent firewall and hardening target.
Is port 135 TCP or UDP?
Port 135 (MS-RPC) uses TCP.
Is port 135 secure?
Port 135 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 135 on my firewall?
Only if you specifically need MS-RPC. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.