Teredo clients, when located behind a restricted NAT, allow remote attackers to establish an inbound connection without the guessing required to find a port…

Teredo clients, when located behind a restricted NAT, allow remote attackers to establish an inbound connection without the guessing required to find a port mapping for a traditional restricted NAT client, by (1) using the client port number contained in the Teredo address or (2) following the bubble-to-open procedure.