- 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.
Port 513: remote login a la telnet; automatic authentication performed based on priviledged port numbers and distributed data bases which identify "authentication domains"
Port 513 is assigned by IANA to login (remote login a la telnet; automatic authentication performed based on priviledged port numbers and distributed data bases which identify "authentication domains"), who (maintains data bases showing who's logged in to machines on a local net and the load average of the machine).
513
How login works
Remote accessThe client opens a session to port 513: 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
- Assigned2 registered services
- Range
- Well-known (0-1023)
- Category
- Remote access
Is port 513 dangerous?
We have no specific security note for port 513. Its risk depends on the program actually listening on it. General advice for remote access services:
IANA registry entries for port 513
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| login | 513 | TCP | remote login a la telnet; automatic authentication performed based on priviledged port numbers and distributed data bases which identify "authentication domains" | - | - |
| who | 513 | UDP | maintains data bases showing who's logged in to machines on a local net and the load average of the machine | - | - |
// source: IANA service name and port number registry
Which program uses port 513, and is it reachable?
Linux
sudo ss -ltnup 'sport = :513' # process listening on 513
sudo lsof -nP -i :513macOS
sudo lsof -nP -i :513
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 513 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 513 netstat -ano | findstr :513
From another machine
nmap -p 513 -sV <host> sudo nmap -sU -p 513 <host> nc -zv <host> 513
Block it in the firewall
sudo ufw deny 513/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 513" -Direction Inbound -LocalPort 513 -Protocol TCP -Action Block # Windows
What is port 513 used for?
Port 513 is assigned by IANA to login (remote login a la telnet; automatic authentication performed based on priviledged port numbers and distributed data bases which identify "authentication domains"), who (maintains data bases showing who's logged in to machines on a local net and the load average of the machine).
Is port 513 TCP or UDP?
Port 513 is registered for TCP and UDP.
Is it safe to open port 513?
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 513 is open?
On Linux run "ss -ltnup 'sport = :513'", on macOS "lsof -nP -i :513", and on Windows "netstat -ano | findstr :513" to see the local process. From another machine, "nmap -p 513 <host>" shows whether it is reachable.
Other remote access ports
: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