Symantec Raptor Firewall 6.5 and 6.5.3, Enterprise Firewall 6.5.2 and 7.0, VelociRaptor Models 500/700/1000 and 1100/1200/1300, and Gateway Security 5110/5200/5300 generate easily predictable initial sequence numbers (ISN), which allows remote attackers to spoof connections.
https://exchange.xforce.ibmcloud.com/vulnerabilities/12836
http://www.symantec.com/techsupp/bulletin/archive/firewall/082002firewall.html
http://www.securityfocus.com/bid/5387
http://archives.neohapsis.com/archives/bugtraq/2002-07/0492.html