Port 512: Rexec
Port 512 is rexec, a legacy protocol for running a command on a remote host that sends the username and password in clear text. It has been replaced by SSH on port 22 for essentially every modern use case.
| Port number | 512 |
|---|---|
| Service | Remote Process Execution |
| Protocol | TCP |
| Category | Remote access |
| Default encryption | No |
How do I check whether port 512 is open?
Port 512 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 512 | 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 512 | 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 ':512 ' | Lists the process bound to port 512 on Linux. On macOS use lsof -nP -iTCP:512 -sTCP:LISTEN, on Windows netstat -ano | findstr :512 |
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 512 used for?
Port 512 is rexec, a legacy protocol for running a command on a remote host that sends the username and password in clear text. It has been replaced by SSH on port 22 for essentially every modern use case.
Is port 512 TCP or UDP?
Port 512 (Rexec) uses TCP.
Is port 512 secure?
Port 512 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 512 on my firewall?
Only if you specifically need Rexec. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.