The UPnP IGD implementation in the Broadcom UPnP stack on the Cisco Linksys WRT54G with firmware before 4.30.5, WRT54GS v1 through v3 with firmware before 4.71.1, and WRT54GS v4 with firmware before 1.06.1 allows remote attackers to establish arbitrary port mappings by sending a UPnP AddPortMapping action in a SOAP request to the WAN interface, related to an "external forwarding" vulnerability.