- Close the port if nothing on the host needs it.
- Identify the process that listens on it (commands below) before opening it in a firewall.
- Expose a service only to the networks that use it.
Port 33: Display Support Protocol
Port 33 is assigned by IANA to dsp (Display Support Protocol).
33
How dsp works
Other servicesThe client sends a request to port 33 and the dsp 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
- Other services
Is port 33 dangerous?
We have no specific security note for port 33. Its risk depends on the program actually listening on it. General advice for other services services:
IANA registry entries for port 33
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| dsp | 33 | TCP, UDP | Display Support Protocol | - | - |
// source: IANA service name and port number registry
Which program uses port 33, and is it reachable?
Linux
sudo ss -ltnup 'sport = :33' # process listening on 33
sudo lsof -nP -i :33macOS
sudo lsof -nP -i :33
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 33 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 33 netstat -ano | findstr :33
From another machine
nmap -p 33 -sV <host> sudo nmap -sU -p 33 <host> nc -zv <host> 33
Block it in the firewall
sudo ufw deny 33/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 33" -Direction Inbound -LocalPort 33 -Protocol TCP -Action Block # Windows
What is port 33 used for?
Port 33 is assigned by IANA to dsp (Display Support Protocol).
Is port 33 TCP or UDP?
Port 33 is registered for TCP and UDP.
Is it safe to open port 33?
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. Close the port if nothing on the host needs it.
How do I check if port 33 is open?
On Linux run "ss -ltnup 'sport = :33'", on macOS "lsof -nP -i :33", and on Windows "netstat -ano | findstr :33" to see the local process. From another machine, "nmap -p 33 <host>" shows whether it is reachable.
Other other services ports
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp