ZyXEL ZyWALL 10 before 3.50 allows remote attackers to cause a denial of service via an ARP packet with the firewall's IP address and an incorrect MAC address, which causes the firewall to disable the LAN interface.
http://www.securityfocus.com/archive/1/261411
http://www.iss.net/security_center/static/8436.php
http://archives.neohapsis.com/archives/vulnwatch/2002-q1/0067.html