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Re: No shell => secure?
From: Barry Fitzgerald <bkfsec () sdf lonestar org>
Date: Fri, 09 Jul 2004 17:34:48 -0400

Ron DuFresne wrote:

        [snip]

This is not security through obscurity. This is security through
incompatibility. The point of the idea is to make it necessary for an
attacker to rewrite an exploit for my system specifically. This is
something that over 99% of the potential attackers would not do, because
they don't care about my system. When you have an exploit that works
against all the RedHat boxes on the Internet, would you bother to
customize it so that it works against one single server of one single
random weirdo? It's not worth it.


beleive and redefine well known terms and methodologies as you wish, it
remains none-the-less as I and others have pointed out nothing more then
security via obscurity.  and bears the dangers as some others have pointed
out that you will most likely end up with an unusable system.  On a number
of vender OS', if the sh shell of csh shell, hooked to root user and
startup scripts is not the expected defaults, those OS's fail to function
properly on and tween reboots.


I think you guys need to stop arguing because you're both right.

Yes, changing the shell executable names is security through obscurity. Yes, it's also security through incompatibility. If he builds the system from scratch, it doesn't matter what other distributions do -- that's irrelivent at that point. It also doesn't matter if he breaks the standard, he can choose to do that if he wants.

Doing this won't stop all potential attacks and it will stop many of the automated attacks that exist in the wild. Those are the facts as they boil down. I think we go a little bit overboard when we say that security through obscurity is bad. I think that we've gained this knee jerk reaction because people try to pass off obscurity as security, but in the end, obscurity can be a useful security tool.

Part of the reason that people deploy firewalls is for obscurity. People munge headers for security. People rename user accounts for obscurity. The very purpose of using encryption is to obscure data. Do these actions stop crackers from gaining access to systems? Do they make them less vulnerable? Not really. They do, however, cause the attacker to increase the amount of time it takes to carry out a successful attack - and that is worth something.

All theory aside, the fact of the matter is that if something takes too much time it will deter *most* people from trying. (I say most people because there's a class of cracker that is actually motivated by a lengthy challenge, but if you've attracted their attention you'd have been cracked regardless of whether obscurity was used.)

Relying on obscurity is bad. We know that closing the source code of a program doesn't make the program more secure. We know that changing the port of your HTTP server doesn't make it immune to compromise. But, to go from that set of points and then to claim that there's no value to any form of obscurity is to make a logical leap that is not supported by strategic fact.

If he's willing to go through the trouble of maintaining his own flavor of GNU/Linux so that he can have renamed programs, then that's his prerogative. It will buy him something. I think tying that to never having been rooted is a stretch, but it isn't of no value at all.

            -Barry

p.s. No offense meant to any party.


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