Re: VML Exploit vs. AV/IPS/IDS signatures

[nirvana <karmic_nirvana () yahoo com>]

Aviv,
  
> There are gateway solutions out there which implement sort-of lexical
> parsers (e.g. www.esafe.com, www.webwasher.com, www.finjan.com).
   
  Isn't it wonderful that we got these wonderful technical solutions? But without even arguing the technical 
capabilities of the above-mentioned products, I believe there's a limit as to how far we can push the envelope, i.e. I 
can't afford to buy "specialized" security tools/devices for "speclialized" attacks unless my company relies heavily on 
web/content services.

> Also, there is no way to "gather the maximum number of exploit variants as
> you can". Because, by using server side scripting to randomize the exploit's
> content, it's unfeasible to collect all possible variants.

  Agreed. I forgot to mention that I have worked for some network-style IPS companies. These mails stem out from my 
experience and frustration in tackling the kind of vulnerabilities we are discussing here. We, as a vendor, would hedge 
our bet on the fact that crackers won't use randomied exploit generators (how many WMF mass-exploitation scenarios used 
gzip+chunked evasion?). Let me confess, as an engineer I always felt as being one-step behind the hackers, but 
sometimes you have to forget the existential angst and just deliver. 
   
  > I really would like to know the source of information which tells you that
> AV solutions provide almost 99% of protection against in-the-wild
> exploits... "Few sources" doesn't necessarily mean few possible variants.

  I wasn't talking about AV solutions. My focus was on one part of the solution, IDS/IPS. In our company, we 
established a information-sharing network with other security companies. So the real-time exploit-facing signatures 
were then subjected to live traffic, honeypots and countless variants; They seemed to work out pretty well. 
  
Thanks,
  Pukhraj

Aviv Raff <avivra () gmail com> wrote:
    Hi, 

There are gateway solutions out there which implement sort-of lexical
parsers (e.g. www.esafe.com, www.webwasher.com, www.finjan.com).
  

Also, there is no way to "gather the maximum number of exploit variants as
you can". Because, by using server side scripting to randomize the exploit's
content, it's unfeasible to collect all possible variants.

I really would like to know the source of information which tells you that
AV solutions provide almost 99% of protection against in-the-wild
exploits... "Few sources" doesn't necessarily mean few possible variants.

-- Aviv.

-----Original Message-----
From: Pukhraj Singh [mailto:pukhraj.singh () gmail com] 
Sent: Tuesday, September 26, 2006 10:40 PM
To: avivra; EArsal () techdata de
Cc: full-disclosure () lists grok org uk; bugtraq () securityfocus com
Subject: Re: VML Exploit vs. AV/IPS/IDS signatures

Avivra,

I acknowledge the research you and Ertunga
(http://www.immunitysec.com/pipermail/dailydave/2006-September/003557.html)
have put up.

Protection against client-side scripting vulnerabilities is the
Achilles' Heel for all network-style IDS/IPS vendors. These languages
offer too much flexibility over the syntax and semantics, thus
becoming the pain-point for the underlying architecture for
network-style IDS/IPS which are better accustomed to analyze
structured data (like protocols and even file-formats). There's is
simply too much you can mutate here and you can't expect vendors to
develop on-the-fly javascript parsers! Thus the protection they
develop is simply a business objective, as they can loose a lot
mileage here if they don't cover vulnerabilities like this one. They
had the same stance for file-format vulnerabilities till they were
forced to add decoding routines for them by the sheer number of new
file-based vulnerabilities which were coming out. AV and local-style
protection is the best defense mechanism here (but even they failed in
this case!).

However, the other way out is to gather the maximum number of exploit
variants as you can (from mutual cooperation between security
companies) and provide real-time exploit-facing protection against
them. This is what they generally do and it provides almost 99%
protection (might surprise many) because most out-in-the-wild exploits
are derived from few sources only.

Thanks,
Pukhraj

On 9/26/06, avivra wrote:
> The code for exploiting the unpatched VML vulnerability is in-the-wild
> for a week or so. This was enough time for Anti Virus, IPS/IDS and
> other reactive security products' vendors to create a signature for
> the in-the-wild exploit.
> So, I put my hand on one of the in-the-wild and tested it using Virus
> Total. The results were not so good. Only 10 of 27 Anti-Viruses
> detected the exploit on the malicious web page.
> Are those signatures generic enough? I've decided to check it out.
>
> I've used 5 simple methods, trying to evade being detected by the
signature:
> 1) I've replaced the location where EIP should jump when the exploit
> is activated, with a different valid address.
> 2) I've replaced the VML element from "rect" with one of the other VML
elements.
> 3) I've replaced the payload with a different valid shell code.
> 4) I've replaced the namespace key with a random key.
> 5) A combination of all of the above.
>
> Please note that when I changed the code using any of the methods, the
> exploit still worked.
>
> More info:
http://aviv.raffon.net/2006/09/25/VMLExploitVsAVIPSIDSSignatures.aspx
> -- Aviv.

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