Common attacks and weaknesses
- Responder-style poisoning captures NTLM hashes on internal networks.
Port 5355: LLMNR
Windows name resolution fallback on the local network.
5355
How LLMNR 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
- 6/10 high 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 5355 dangerous?
How to secure it
- Disable LLMNR and NetBIOS name resolution by Group Policy.
IANA registry entries for port 5355
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| llmnr | 5355 | TCP, UDP | LLMNR | - | 2004-06 |
// source: IANA service name and port number registry
Which program uses port 5355, and is it reachable?
Linux
sudo ss -ltnup 'sport = :5355' # process listening on 5355
sudo lsof -nP -i :5355macOS
sudo lsof -nP -i :5355
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5355 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 5355 netstat -ano | findstr :5355
From another machine
nmap -p 5355 -sV <host> sudo nmap -sU -p 5355 <host> nc -zv <host> 5355
Block it in the firewall
sudo ufw deny 5355/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 5355" -Direction Inbound -LocalPort 5355 -Protocol TCP -Action Block # Windows
What is port 5355 used for?
Windows name resolution fallback on the local network.
Is port 5355 TCP or UDP?
Port 5355 is registered for UDP and TCP. In practice the service mostly uses UDP.
Is it safe to open port 5355?
It is rated 6/10 (high) when exposed to the Internet. Responder-style poisoning captures NTLM hashes on internal networks. Disable LLMNR and NetBIOS name resolution by Group Policy.
How do I check if port 5355 is open?
On Linux run "ss -ltnup 'sport = :5355'", on macOS "lsof -nP -i :5355", and on Windows "netstat -ano | findstr :5355" to see the local process. From another machine, "nmap -p 5355 <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