The Danish AI-Sec Reports:

There exists a problem in Simple, secure webserver 1.1 which is shipped with Raptor Firewall 6.5 (among others), in which an attacker can connect to the proxyserver from the outside, and issue a CONNECT to IP-addresses on the inside interface, and thereby determine if there are hosts present or not by inspecting the errormessage. This problem lets an attacker map out the entire topology of a client from the outside.

Symantec has addressed this issue as a collateral problem in an earlier security update for the Symantec Enterprise Firewall. The Symantec Enterprise Firewall is not vulnerable to this concern if patched fully up-to-date.

Versions affected:
Raptor Firewall 6.5 (Windows NT)
Raptor Firewall V6.5.3 (Solaris)
Symantec Enterprise Firewall 6.5.2 (Windows 2000 and NT)
Patches are available.