Re: HTTP Parameter Pollution

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

Stephen, 

thanks for your comments. We appreciate it very much. 

Speaking about the server side exploitation of HPP, we have defined HPP
as the feasibility to override or add HTTP GET/POST parameters by
injecting query string delimiters. 

Considering: 

1). A front end web server (A) which directly communicates with the
client and
2). A back end web server (B) which is accessed by (A) via a GET or POST
request, and some of the request values are controlled by an attacker.

We may imagine the following example, as reported in the slides: 

// Code on (A): 
void private executeBackendRequest(HTTPRequest request){ 

String amount=request.getParameter("amount"); 
String beneficiary=request.getParameter("recipient"); 

// This connects to (B)
HttpRequest("http://backendServer.com/servlet/actions","POST";,
"action=transfer&amount="+amount+"&recipient="+beneficiary); }

Here, there is a component (A) acting as a dispatcher for (B). In
addition, there's also an "action=transfer" key value pair which is
hardcoded. 

In this case, the attacker may inject something like 
recipient=Mat%26action%3dwithdraw 

On (A), it will be concatenated resulting in a new payload:

action=transfer&amount=1000&recipient=Mat&action=withdraw 

which will be sent to (B) by (A). 

As you can notice the parameter action has been injected and, in case
(B) gets the last occurrence only (see server enumeration) then, the
action will be "withdraw" instead of "transfer". 

In this case, we think that the given HPP definition properly fits since
it adds or overrides an HTTP parameter.

Let us know if we correctly understood your question.

Cheers,
Stefano

Il giorno mar, 19/05/2009 alle 15.30 +0200, Stephen de Vries ha scritto:
> Guys,
>
> A nice piece of research!  A comment on the slides "HPP Server Side  
> Attacks 1/2 and 2/2", I don't think that that case fits into the  
> definition of HPP.  It looks more like standard parameter manipulation  
> because it doesn't depend on the request having multiple parameters.
>
>
> Stephen
>
>
>
> > On May 19, 2009, at 1:52 PM, Stefano Di Paola 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
> > > ..................
> >
> > -- 
> > Stephen de Vries
> > Corsaire Ltd
> > E-mail: stephen () corsaire com
> > Tel:        +44 1483 746714
> > Fax:        +44 1483 746701
> > Web:        http://www.corsaire.com
--  

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
..................