[12065] in bugtraq
FireWall-1 weakness
daemon@ATHENA.MIT.EDU (Hugo.van.der.Kooij@CAIW.NL)
Thu Sep 30 13:51:23 1999
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Message-Id: <Pine.LNX.4.10.9909300738360.31066-100000@bastion.nl3155vj16.vanderkooij.org>
Date: Thu, 30 Sep 1999 07:58:22 +0200
Reply-To: Hugo.van.der.Kooij@CAIW.NL
From: Hugo.van.der.Kooij@CAIW.NL
X-To: BUGTRAQ@SECURITYFOCUS.COM
To: BUGTRAQ@SECURITYFOCUS.COM
Hi,
At present CheckPoint has not seen any reason to see the following issue
as a weakness in their product. So I now report this here:
If one takes CheckPoint FireWall-1 v4.0 SP4 (latest version) and build the
following rule:
Source: Destination: Protocol: Action:
Any citrix-server winframe accept
Where citrix-server is a simple network object and winframe the definition
as created by CheckPoint.
This rules allows winframe sessions to pass but should stop other traffic
as it does some more packet analyses.
A customer tried to run FTP through it and saw an accept in the log. But
due to the lack of a server on the other side could not establish wether
or not there was a leak.
Recreating this in the lab with telnet showed the same. However putting a
working telnetd on port 1494 at the specific server did still not allow
anyone to enter the system. After initial TCP connection setup it seems
the firewall drops connections.
But this will lead to two weaknesses:
1. Any server defended by FireWall-1 could be subject to a DoS attack if
the server should accept TCP sessions at port 1494. The server allows
the initial setup and then stops forwarding.
(That's two dependencies but we are the people that allways assume the
worst as we are the ones that try to do the worst in such case ;-)
2. The log only shows a succesfull start of the session but down not
indicate any filtering. This leaves the operator of the firewall in
the dark wether or not a session was cut off due to the missing
winframe signature. So there is no indication off foul play and
everyone will be assuming things are just fine.
(We all know that if a firewall is supposed to show dropped packets
that plenty of people will never look for trouble in the sessions that
are allowed.)
I hope that this document will help people understand a oversight in the
logging/alerting facilities that they have to deal with in FireWall-1.
I did not test for other types of services that have additional checks in
them. They may suffer the same lack of logging/alerting in case incorrect
sessions are blocked.
Regards,
Hugo.
--
Hugo van der Kooij; Oranje Nassaustraat 16; 3155 VJ Maasland
hvdkooij@caiw.nl http://home.kabelfoon.nl/~hvdkooij/
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