source: http://www.securityfocus.com/bid/7021/info

A vulnerability has been reported in the 3Com Superstack 3 Firewall. HTTP content filters put in place by the device fail to assemble fragmented data, potentially allowing an attacker to access unauthorized web sites.

An attacker could exploit this vulnerability by connecting a web server using a protocol in which data is fragmented when transferred.

Although unconfirmed, it is possible that this issue also affects other HTTP content filters. 

telnet www.blockedsite.com 80

GET / HTTP/1.1
Host: www.blockedsite.com