WatchGuard SOHO products running firmware 5.1.6 and earlier, and Vclass/RSSA using 3.2 SP1 and earlier, allows remote attackers to bypass firewall rules by sending a PASV command string as the argument of another command to an FTP server, which generates a response that contains the string, causing IPFilter to treat the response as if it were a legitimate PASV command from the server.