Port Authority Edition – Internet Vulnerability Profiling
by Steve Gibson,  Gibson Research Corporation.

Goto Port 1719
Probe Port 1720
Enter Port: 0-65535
Goto Port 1721

Port Authority Database

Port 1720


H.323 (Microsoft NetMeeting) call setup protocol

Port 1720 is used by the H.323 teleconferencing protocol (most commonly encountered in Microsoft NetMeeting) during call setup negotiation.

Related Ports: 
389, 1002

Background and Additional Information:

Users running Microsoft NetMeeting may discover that their ports 1720 (and 389) are open and exposed to the Internet. This should be regarded as something of a security danger since denial of service exploits for port 1720 and the H.323 protocol have been developed in the past and others could be discovered in the future.

The best policy and practice is to only run NetMeeting, or any other H.323 teleconferencing system, when it is explicitly needed. Alternatively, a NAT router or personal firewall could be configured to keep ports 1720 and 389 closed until they are needed for NetMeeting conferencing.

Note: NetMeeting's H.323 teleconferencing protocol is extremely NAT router and firewall hostile due to its dynamic assignment of UDP protocol ports for media content streaming. Any network appliance or filtering software must be highly protocol aware to provide effective protection while allowing the protocol to function. You should verify that any NAT router or personal firewall is capable of managing NetMeeting conference connections before investing in any such product's purchase.

For further reading or research:



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