Great Circle Associates Firewalls
(October 1997)
 

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Subject: Re: DNS on the Firewall - security problem
From: Adam Shostack <adam @ homeport . org>
Date: Sun, 12 Oct 1997 01:41:38 -0400 (EDT)
To: ahuger @ silence . secnet . com
Cc: firewall-wizards @ nfr . com, firewalls @ greatcircle . com (Firewalls mailing list)
In-reply-to: <Pine . BSI . 3 . 96 . 971010140951 . 3687A-100000 @ silence . secnet . com> from Alfred Huger at "Oct 10, 97 02:12:22 pm"

Alfred is absolutely right.  I forgot how little what I first wrote
references this; I've added a paragraph to make more clear that this
is not a real fix, but a temporary hack.

I'm working on a paper on the topic of DNS, and working on some kernel
hacks to allow a special user or group (other than root) to bind to
low numbered ports.  Another way to deal with the problem is to use a
packet filter that does port translation so that the DNS server can
live on a high numbered port (eg, 5353), and still appear to be on
port 53.  Both these allow you to run the DNS server as an unprivleged
user in a chroot jail.

Sorry, the kernel kludges are not available.

Adam


Alfred Huger wrote:
| 
| > there is no egg* to overflow and break a chroot.  Thus, if you don't
| > put CHROOT/bin/sh in place, the standard attacks will fail, but a
| > smart attacker can still get in.  In practicality, there are few smart
| > attackers.
| > 
| 
| It only takes *one* smart attacker with a subscription to Bugtraq and a
| predeliction to share his or her work. The l0pht (which you referanced) is
| a perfect example of this.  



-- 
"It is seldom that liberty of any kind is lost all at once."
					               -Hume




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