Common attacks and weaknesses
- Information leaks about devices; amplification when reachable from the Internet.
Port 5353: mDNS
Local service discovery (Bonjour, Avahi).
5353
How mDNS works
Network servicesA device asks the whole local network a question and the device that matches answers. It travels in clear text: anyone on the path can read it.
- Transport
- UDP · TCP
- Exposure risk
- 4/10 moderate if reachable from the Internet
- Encryption
- Clear textreadable on the network
- IANA status
- Assigned1 registered service
- Range
- Registered (1024-49151)
- Category
- Network services
Is port 5353 dangerous?
How to secure it
- Block from outside the local network.
IANA registry entries for port 5353
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| mdns | 5353 | TCP, UDP | Multicast DNS | RFC 6762 | - |
// source: IANA service name and port number registry
Which program uses port 5353, and is it reachable?
Linux
sudo ss -ltnup 'sport = :5353' # process listening on 5353
sudo lsof -nP -i :5353macOS
sudo lsof -nP -i :5353
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5353 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 5353 netstat -ano | findstr :5353
From another machine
nmap -p 5353 -sV <host> sudo nmap -sU -p 5353 <host> nc -zv <host> 5353
Block it in the firewall
sudo ufw deny 5353/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 5353" -Direction Inbound -LocalPort 5353 -Protocol TCP -Action Block # Windows
What is port 5353 used for?
Local service discovery (Bonjour, Avahi).
Is port 5353 TCP or UDP?
Port 5353 is registered for UDP and TCP. In practice the service mostly uses UDP.
Is it safe to open port 5353?
It is rated 4/10 (moderate) when exposed to the Internet. Information leaks about devices; amplification when reachable from the Internet. Block from outside the local network.
How do I check if port 5353 is open?
On Linux run "ss -ltnup 'sport = :5353'", on macOS "lsof -nP -i :5353", and on Windows "netstat -ano | findstr :5353" to see the local process. From another machine, "nmap -p 5353 <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 :5355 LLMNR udp · tcp · high risk