7/TCP/UDP - Pentesting Echo Service

Basic Information

The Echo Protocol is a diagnostic service that returns received data to its sender. RFC 862 defines both a TCP service and a UDP service on port 7.^[1]

Default ports: 7/TCP and 7/UDP

PORT  STATE SERVICE
7/udp open  echo
7/tcp open  echo

An exposed UDP echo service can participate in a denial-of-service loop if it is made to exchange traffic with another UDP character-generating service. CERT’s advisory recommends disabling unnecessary UDP diagnostic services and filtering spoofed traffic.^[2]

Contact the UDP Echo Service

nc -uvn <IP> 7
Hello echo    # Sent by the client
Hello echo    # Returned by the server

Shodan

port:7 echo

References

• [1] RFC 862 - Echo Protocol
• [2] CERT Advisory CA-1996-01 - UDP Port Denial-of-Service Attack