Vulnerability Development: Re: Obfuscated shellcode

[Aaron Turner <aturner () pobox com>]

Don,

While most IDS's will detect a NOOP sled, any IDS worth it's salt which has
a signature for an exploit won't rely on it.  Rather it will use something
unique to the exploit which can't (at least easily) changed to avoid 
detection.

Also, in my experiance most corporations update their signatures about as
often as feasible (a combination of how often the IDS vendor updates the
signatures and how easy it is to push the update to the sensors).  Any
organization which isn't using the latest signature set is wasting their
effort and $$$.  Ie, if you have to carefully manage your signature set 
and delay updating your sensors because things might horribly break 
without a way to manage that risk, then you should find another IDS 
vendor.

-- 
Aaron Turner <aturner at pobox.com|synfin.net>  http://synfin.net/
They that can give up essential liberty to obtain a little temporary 
safety deserve neither liberty nor safety. -- Benjamin Franklin
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On Sun, Feb 01, 2004 at 12:38:32PM -0500, Don Parker wrote:
> Hello all, do any of you bother using obfuscated eggs during a pentest? I ask here for I 
> got no responses elsewhere. Though changing the well known x90 sled to some other 1 byte 
> function that won't affect the egg won't work against a patched service it will, however 
> elude an IDS signature.  
>  
> Quite a few large corporations may get updated signatures relatively quickly but, they 
> often do not patch for sometime due to baseline rollouts. Hence using an obfuscated egg 
> to slip past the IDS. This technique is not new, but it is becoming more well known. 
> There are some mitigaing factors here which could affect this such as application layer 
> firewalls and the such. I would however be interested in your thoughts on this. I have 
> not seem much discussion anywhere on this topic.

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