Common attacks and weaknesses
- Packet loops with chargen (fraggle attacks).
Port 7: Echo
Echo test service.
7
How Echo works
Network servicesThe client sends a request to port 7 and the Echo service answers. It travels in clear text: anyone on the path can read it.
- Transport
- TCP · UDP
- Exposure risk
- 4/10 moderate if reachable from the Internet
- Encryption
- Clear textreadable on the network
- IANA status
- Assigned1 registered service
- Range
- Well-known (0-1023)
- Category
- Network services
Is port 7 dangerous?
How to secure it
- Disable it.
IANA registry entries for port 7
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| echo | 7 | TCP, UDP | Echo | - | - |
// source: IANA service name and port number registry
Which program uses port 7, and is it reachable?
Linux
sudo ss -ltnup 'sport = :7' # process listening on 7
sudo lsof -nP -i :7macOS
sudo lsof -nP -i :7
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 7 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 7 netstat -ano | findstr :7
From another machine
nmap -p 7 -sV <host> sudo nmap -sU -p 7 <host> nc -zv <host> 7
Block it in the firewall
sudo ufw deny 7/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 7" -Direction Inbound -LocalPort 7 -Protocol TCP -Action Block # Windows
What is port 7 used for?
Echo test service.
Is port 7 TCP or UDP?
Port 7 is registered for TCP and UDP.
Is it safe to open port 7?
It is rated 4/10 (moderate) when exposed to the Internet. Packet loops with chargen (fraggle attacks). Disable it.
How do I check if port 7 is open?
On Linux run "ss -ltnup 'sport = :7'", on macOS "lsof -nP -i :7", and on Windows "netstat -ano | findstr :7" to see the local process. From another machine, "nmap -p 7 <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