Re: Cracking a server without services

From: Warwick Poole (warwick-lists@globalvision.com)
Date: 07/12/02


From: Warwick Poole <warwick-lists@globalvision.com>
To: Jeff Aufderheide <j.aufderheide@attbi.com>, security-basics@securityfocus.com
Date: 12 Jul 2002 15:52:38 +0100

On the point of Fragrouter being able to use fragments to bypass
packetfiltering firewalls, could you not use a rule like

iptables -A INPUT -i eth0 -f -j DROP

to drop fragments on the perimeter router, thus preventing fragrouter
from being able to do this?

As far as I know, the only reason for fragments would be for NFS
services, which I would never want to cross my perimeter router anyway.

Warwick

On Thu, 2002-07-11 at 23:06, Jeff Aufderheide wrote:
> In-Reply-To: <3D2D39C2.11150.19DF84@localhost>
>
> Hi Mr.Bremer-
> I just thought I would give some info about getting past a packet
> filtering firewall. It is not as difficult as one would think. All you
> would need is the right tool. And......that tool is called Frag Router.
> It is in my estimation that this program can get past 2/3 IDS and Packet
> filtering Devices. Although there are plans in the works to correct this
> issue by implementing an IDS system on both host and destination boxes
> (very expensive indeed).
>
> Now to answer the other gentlemen's question. And, someone correct me if
> I'm wrong, But the only conceivable way to gain access to a computer
> without any services running would be gaining local access to the box
> itself and logging in as admin or a user account. From there, depending
> on which OS you want to take advantage of (for example MS2k) you could
> boot into DOS or a version of Linux and download the SAM file to a floppy
> disk. If all of your ports are closed you will not communicate to anyone
> in the world, Nothing in - Nothing out.
>
> I hope this answers your questions.
>
> V/R
>
> Jeff Aufderheide
>
> Unfortunately I can't point you to any information regarding this, but I
> can offer a little input. Cracking a machine with no services running
> would be VERY difficult indeed (I wouldn't say "impossible" though).
> Machines that are used as a packet filtering firewall fall into this
> category.
>
> What is more likely to happen than cracking the machine itself is
> finding a problem in the packet filtering rules that would allow a
> cracker unauthorized access to a host that is being protected by the
> firewall. On rare occasions, there may even be a bug in the packet
> filtering code itself that could create the same problem.
>
> Steve Bremer
>



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