- Restrict management and monitoring protocols to the monitoring network.
- Replace community strings and default credentials.
- Send logs over TLS.
Port 5666: Nagios Remote Plugin Executor
Port 5666 is assigned by IANA to nrpe (Nagios Remote Plugin Executor).
5666
How nrpe works
Monitoring & loggingThe monitoring server collects metrics, alerts or logs from devices over port 5666.
- Transport
- TCP
- Exposure risk
- not rated depends on the program listening
- Encryption
- Unknownnot stated by the registry
- IANA status
- Assigned1 registered service
- Range
- Registered (1024-49151)
- Category
- Monitoring & logging
Is port 5666 dangerous?
We have no specific security note for port 5666. Its risk depends on the program actually listening on it. General advice for monitoring & logging services:
IANA registry entries for port 5666
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| nrpe | 5666 | TCP | Nagios Remote Plugin Executor | - | 2017-09-06 |
| - | 5666 | - | Reserved | - | - |
// source: IANA service name and port number registry
Which program uses port 5666, and is it reachable?
Linux
sudo ss -ltnup 'sport = :5666' # process listening on 5666
sudo lsof -nP -i :5666macOS
sudo lsof -nP -i :5666
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5666 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 5666 netstat -ano | findstr :5666
From another machine
nmap -p 5666 -sV <host> nc -zv <host> 5666
Block it in the firewall
sudo ufw deny 5666/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 5666" -Direction Inbound -LocalPort 5666 -Protocol TCP -Action Block # Windows
What is port 5666 used for?
Port 5666 is assigned by IANA to nrpe (Nagios Remote Plugin Executor).
Is port 5666 TCP or UDP?
Port 5666 is registered for TCP.
Is it safe to open port 5666?
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. Restrict management and monitoring protocols to the monitoring network.
How do I check if port 5666 is open?
On Linux run "ss -ltnup 'sport = :5666'", on macOS "lsof -nP -i :5666", and on Windows "netstat -ano | findstr :5666" to see the local process. From another machine, "nmap -p 5666 <host>" shows whether it is reachable.
Other monitoring & logging ports
:161 SNMP udp · tcp · high risk :162 SNMP trap udp · tcp · moderate risk :9090 Prometheus / admin consoles tcp · udp · high risk :514 Syslog udp · tcp · moderate risk :6514 Syslog over TLS tcp · udp · dccp · low risk :5601 Kibana tcp · udp · high risk :391 SynOptics SNMP Relay Port tcp · udp :412 Trap Convention Port tcp · udp