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Re: Buffer overflow prevention
From: Shaun Clowes <shaun () securereality com au>
Date: Mon, 18 Aug 2003 09:09:45 +1000

On Fri, Aug 15, 2003 at 11:48:14AM -0700, Crispin Cowan wrote:
Shaun Clowes wrote:

Perhaps I'm the only one who feels this way, but I believe that the vast
majority of the exploitation of systems is being performed by people
with no knowledge of how to write an exploit and that the vast majority
of exploits are fragile. Doing anything that makes you different from
every other installation of Linux/HPUX/Solaris/InsertOSHere will
drastically decrease the changes of any point and click exploit working
against you.

Could a determined (and knowledgable) attacker still get through? Sure.
But if we're talking protections that take very little effort to
implement, have a minor performance impact and will save your
skin some of the time, it's obvious that it's worth deploying them. As
long as you're not kidding yourself that you're then totally secure.

Exactly: trivial changes will protect you from script kiddies. 
Non-bypassability is required to protect you from determined attackers. 
It depends on your threat model: how much will a penetration event cost 
you? What is it worth to someone to hack you?

Well, you've immediately eliminated 90% or more of the threat, so it's a
good start. In any case, if we are talking about the famous determined
attacker it's reasonable to assume that they are going to get you no
matter what you do and that you need to carefully consider methods of
reducing the damage from intrusion (rather than betting on stopping the
intrusion all together).

Its kind of reminiscent of that old joke about the two guys running away
from the lion. You don't have to beat the lion, just the other person. 

But if you taste better (you are a bank and he is a basement RH box) 
then the lion may choose to chase you anyway.

If I'm the bank I'm probably running Solaris, HP-UX, AIX, Irix etc, in
which case I don't even have the option of PaX etc. I would deploy any
kind of protection technology I could find (including non-executable
stack, moved library images etc). 

There is no such thing as a perfect protection, and most of the
protection technologies that have been discussed in this thread are
worth considering. It would seem most pragmatic to deploy whatever you
can in your environment.

I think it's generally accepted that homogenity breeds insecurity, in
which case it makes sense to try to be as different from everyone else
as possible even if that doesn't make it impossible for someone to break
you.

Cheers,
Shaun


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