- Answer only the networks that need the service (no open resolvers, relays or reflectors).
- UDP services can be abused for DDoS amplification: rate-limit or block them at the edge.
- Disable legacy test services that have no use in production.
Port 37: Time
Port 37 is assigned by IANA to time (Time).
37
How time works
Network servicesThe client sends a request to port 37 and the time service answers.
- Transport
- TCP · UDP
- 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
- Network services
Is port 37 dangerous?
We have no specific security note for port 37. Its risk depends on the program actually listening on it. General advice for network services services:
IANA registry entries for port 37
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| time | 37 | TCP, UDP | Time | - | - |
// source: IANA service name and port number registry
Which program uses port 37, and is it reachable?
Linux
sudo ss -ltnup 'sport = :37' # process listening on 37
sudo lsof -nP -i :37macOS
sudo lsof -nP -i :37
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 37 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 37 netstat -ano | findstr :37
From another machine
nmap -p 37 -sV <host> sudo nmap -sU -p 37 <host> nc -zv <host> 37
Block it in the firewall
sudo ufw deny 37/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 37" -Direction Inbound -LocalPort 37 -Protocol TCP -Action Block # Windows
What is port 37 used for?
Port 37 is assigned by IANA to time (Time).
Is port 37 TCP or UDP?
Port 37 is registered for TCP and UDP.
Is it safe to open port 37?
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. Answer only the networks that need the service (no open resolvers, relays or reflectors).
How do I check if port 37 is open?
On Linux run "ss -ltnup 'sport = :37'", on macOS "lsof -nP -i :37", and on Windows "netstat -ano | findstr :37" to see the local process. From another machine, "nmap -p 37 <host>" shows whether it is reachable.
Other network services ports
:53 DNS tcp · udp · moderate risk :135 MS RPC tcp · udp · high risk :123 NTP udp · tcp · moderate risk :67 DHCP server udp · tcp · moderate risk :111 rpcbind tcp · udp · high risk :9100 Raw printing (JetDirect) tcp · udp · high risk :631 IPP / CUPS tcp · udp · high risk :5353 mDNS udp · tcp · moderate risk