Flaw caused by default rulesets in many desktop firewalls under windows

From: Christian decoder Holler (christian_holler@web.de)
Date: 05/10/02


Date: 10 May 2002 18:44:15 -0000
From: Christian decoder Holler <christian_holler@web.de>
To: bugtraq@securityfocus.com


('binary' encoding is not supported, stored as-is)

Several Desktop-Firewalls for Windows, such as Tiny
Personal Firewall 2.0 or ATGuard, maybe also others, allow
DNS resolving by default. That allows reversed trojans to
connect to a server on port 53 and send/receive commands
and informations without the user knowing it. The firewall
permits any communication to any server on port 53 UDP. I
wrote a small trojan in VB and tested it with Tiny Personal
Firewall 2.0 and it worked.

Solution: Change the default rules for DNS to a fixed host,
for example to the DNS server of the ISP or the DNS server
in the local network.

cu
Chris (decoder)