Re: [PATCH] OpenBSD Networking-related randomization port

On Fri, 28 Jan 2005 18:47:55 +0100
Lorenzo Hernández García-Hierro [off-list ref] wrote:

El vie, 28-01-2005 a las 18:40 +0100, Adrian Bunk escribió:

quoted

On Fri, Jan 28, 2005 at 06:17:17PM +0100, Lorenzo Hernández García-Hierro wrote:

quoted

...
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	[off-list ref]