- Keep directory and authentication services on internal networks.
- Require signing or TLS and disable anonymous queries.
- Monitor authentication failures for spraying and brute force.
Port 300: TLS Secure Login Host Protocol (TACACSS)
Port 300 is assigned by IANA to tacacss (TLS Secure Login Host Protocol (TACACSS)).
300
How tacacss works
Directory & authenticationThe client proves who it is on port 300 and gets an answer (or a ticket) it can use with other services.
- Transport
- TCP
- Exposure risk
- not rated depends on the program listening
- Encryption
- Unknownnot stated by the registry
- IANA status
- Assigned1 registered service
- Range
- Well-known (0-1023)
- Category
- Directory & authentication
Is port 300 dangerous?
We have no specific security note for port 300. Its risk depends on the program actually listening on it. General advice for directory & authentication services:
IANA registry entries for port 300
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| tacacss | 300 | TCP | TLS Secure Login Host Protocol (TACACSS) | RFC 9887 | 2025-07-15 |
| - | 300 | - | Reserved | - | - |
// source: IANA service name and port number registry
Which program uses port 300, and is it reachable?
Linux
sudo ss -ltnup 'sport = :300' # process listening on 300
sudo lsof -nP -i :300macOS
sudo lsof -nP -i :300
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 300 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 300 netstat -ano | findstr :300
From another machine
nmap -p 300 -sV <host> nc -zv <host> 300
Block it in the firewall
sudo ufw deny 300/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 300" -Direction Inbound -LocalPort 300 -Protocol TCP -Action Block # Windows
What is port 300 used for?
Port 300 is assigned by IANA to tacacss (TLS Secure Login Host Protocol (TACACSS)).
Is port 300 TCP or UDP?
Port 300 is registered for TCP.
Is it safe to open port 300?
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. Keep directory and authentication services on internal networks.
How do I check if port 300 is open?
On Linux run "ss -ltnup 'sport = :300'", on macOS "lsof -nP -i :300", and on Windows "netstat -ano | findstr :300" to see the local process. From another machine, "nmap -p 300 <host>" shows whether it is reachable.
Other directory & authentication ports
:389 LDAP tcp · udp · high risk :636 LDAPS tcp · udp · moderate risk :88 Kerberos tcp · udp · high risk :3268 Global Catalog (LDAP) tcp · udp · high risk :1812 RADIUS udp · tcp · moderate risk :31 MSG Authentication tcp · udp :49 Login Host Protocol (TACACS) tcp · udp :56 XNS Authentication tcp · udp