Re: HTTP Parameter Pollution

[Stefano Di Paola <stefano.dipaola () wisec it>]

Hi Ivan,

HPP is an input validation vulnerability and, consequentially a 
possible attack, triggered by injection flaws in the context of 
generating QueryStrings/POST payloads. 

If you have only an injection (server or client side) in the context of
query string construction, it doesn't mean you can actually override
hardcoded parameters' values because of web server behaviour.
On the other hand, if you know the web server/application behaviour and
you cannot inject any parameter then you are obviously safe.

So you need both hypothesis in order to exploit the issue.

The main topic is that after identifying the application behaviour in
managing multiple occurrences and considering which are the layers data
passes through, an attacker could exploit the parameter injection
vulnerability. And this is HPP.

I hope we answered your question. 
However within the whitepaper, we are going to explain everything in
detail and likely, we will be able to show the essence of this flaw.

Cheers,
Stefano & Luca

Il giorno mer, 20/05/2009 alle 10.06 +0200, Ivan Ristic ha scritto:
> Hi Stefano,
>
> Your presentation discusses two separate issues:
>
> 1. The differences in how various components handle multiple request
> parameters with the same name when an application expects only one
> (parameter).
> 2. Attacks against query string construction flaws in applications.
>
> Just from reading the slides I couldn't determine which is the main
> topic, and which is the one you named HPP?
>
>
> On Tue, May 19, 2009 at 1:52 PM, Stefano Di Paola
> <stefano.dipaola () wisec it> wrote:
> > Hi guys,
> >
> > during OWASP AppSec Poland 2009 we presented a newly discovered input
> > validation vulnerability called "HTTP Parameter Pollution" (HPP).
> >
> > Basically, it can be defined as the feasibility to override or add HTTP
> > GET/POST parameters by injecting query string delimiters.
> >
> > In the last months, we have discovered several real world flaws in which
> > HPP can be used to modify the application behaviors, access
> > uncontrollable variables and even bypass input validation checkpoints
> > and WAFs rules.
> >
> > Exploiting such HPP vulnerabilities, we have found several problems in
> > some Google Search Appliance front-end scripts, Ask.com, Yahoo! Mail
> > Classic and many other products.
> >
> > If you are interested, you are kindly invited to have a look at:
> > http://www.owasp.org/images/b/ba/AppsecEU09_CarettoniDiPaola_v0.8.pdf
> >
> > We're going to release additional materials in the next future,
> > including a video of the Yahoo! attack vector.
> >
> > Stay tuned on http://blog.mindedsecurity.com and
> > http://blog.nibblesec.org
> >
> > Cheers,
> > Stefano Di Paola and Luca Carettoni
> >
> > --
> > Stefano Di Paola
> > Chief Technology Officer, LA/ISO27001
> > Minded Security Research Labs Director
> >
> > Minded Security - Application Security Consulting
> >
> > Official Site: www.mindedsecurity.com
> >
> > Personal Blog: www.wisec.it/sectou.php
> > ..................
-- 
...oOOo...oOOo....
Stefano Di Paola
Software & Security Engineer

Owasp Italy R&D Director

Web: www.wisec.it
..................