- 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 113: Authentication Service
Port 113 is assigned by IANA to auth (Authentication Service), ident ().
113
How auth works
Directory & authenticationThe client proves who it is on port 113 and gets an answer (or a ticket) it can use with other services.
- 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
- Directory & authentication
Is port 113 dangerous?
We have no specific security note for port 113. Its risk depends on the program actually listening on it. General advice for directory & authentication services:
IANA registry entries for port 113
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| auth | 113 | TCP, UDP | Authentication Service | - | - |
| ident | 113 | TCP | - | - |
// source: IANA service name and port number registry
Which program uses port 113, and is it reachable?
Linux
sudo ss -ltnup 'sport = :113' # process listening on 113
sudo lsof -nP -i :113macOS
sudo lsof -nP -i :113
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 113 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 113 netstat -ano | findstr :113
From another machine
nmap -p 113 -sV <host> sudo nmap -sU -p 113 <host> nc -zv <host> 113
Block it in the firewall
sudo ufw deny 113/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 113" -Direction Inbound -LocalPort 113 -Protocol TCP -Action Block # Windows
What is port 113 used for?
Port 113 is assigned by IANA to auth (Authentication Service), ident ().
Is port 113 TCP or UDP?
Port 113 is registered for TCP and UDP.
Is it safe to open port 113?
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 113 is open?
On Linux run "ss -ltnup 'sport = :113'", on macOS "lsof -nP -i :113", and on Windows "netstat -ano | findstr :113" to see the local process. From another machine, "nmap -p 113 <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