To: linux-kernel@vger.kernel.org
From: Stephen Hemminger <shemminger@osdl.org>
Subject: Re: [PATCH] OpenBSD Networking-related randomization port
Date: Fri, 28 Jan 2005 10:18:25 -0800
Organization: Open Source Development Lab
Message-ID: <20050128101825.388990a0@dxpl.pdx.osdl.net>
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On Fri, 28 Jan 2005 18:47:55 +0100
Lorenzo Hern?ndez Garc?a-Hierro <lorenzo@gnu.org> wrote:

> El vie, 28-01-2005 a las 18:40 +0100, Adrian Bunk escribi?:
> > On Fri, Jan 28, 2005 at 06:17:17PM +0100, Lorenzo Hern?ndez Garc?a-Hierro wrote:
> > >...
> > > As it's impact is minimal (in performance and development/maintenance
> > > terms), I recommend to merge it, as it gives a basic prevention for the
> > > so-called system fingerprinting (which is used most by "kids" to know
> > > how old and insecure could be a target system, many time used as the
> > > first, even only-one, data to decide if attack or not the target host)
> > > among other things.
> > >...
> > 
> > "basic prevention"?
> > I hardly see how this patch makes OS fingerprinting by e.g. Nmap 
> > impossible.
> 
> That's an example, as you can find at the grsecurity handbook [1]:
> 
> "The default Linux TCP/IP-stack has some properties that make it more
> vulnerable to prediction-based hacks. By randomizing several items,
> predicting the behaviour will be a lot more difficult."

No it just changes the fingerprint table.  "Hmm, this looks like a
newer generation system, must be OpenBSD or Linux".

> "Randomized IP IDs hinders OS fingerprinting and will keep your machine
> from being a bounce for an untraceable portscan."
> 
> References:
>  [1]: http://www.gentoo.org/proj/en/hardened/grsecurity.xml

This is a very transitory effect, it works only because your machine
is then different from the typical Linux machine; therefore the scanner
will go on to the next obvious ones. But if this gets incorporated widely
then the rarity factor goes away and this defense becomes useless.

-- 
Stephen Hemminger	<shemminger@osdl.org>

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