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RE: Sanctum AppScan 4 misses potential vulnerabilities in wrapped links
From: "Dawes, Rogan (ZA - Johannesburg)" <rdawes () deloitte co za>
Date: Fri, 26 Sep 2003 09:35:46 +0200

I am inclined to agree with Sanctum's position here. Without actually
executing the javascript, and triggering all the possible events, and
tracing the javascript (in a sandbox, maybe), it is pretty much impossible
to identify the fact that the function called would result in a new URL to
investigate.

For example, the page could include a function to redirect to the SSL
version of a site by getting the web site name from the location bar,
prepending https:// to it, and appending the supplied path.

There are only really three ways of discovering the resulting URL. 

1. Browse it yourself through a monitoring proxy, and let your browser
execute the script.
2. Let the application extract all Javascript and javascript hrefs, and let
the observer decode them manually, and enter URL's.
3. Identify all "entry points" [1] from which javascript can be triggered,
and execute each and every script in a sandbox to observe any URL's that get
constructed.

1. is Sanctum's solution
2. is very manual and intensive, but the user should arguably be reviewing
the javascripts anyway.
3. is the ideal situation, in my mind, but I think that it is a bit
unreasonable to expect at this point. It would be a really good selling
point, though!

3. is still never going lead to a complete replacement for an intelligent
operator, though. There may very easily be situations in which there are
interactions between components in a page or form, javascripts, etc that
would be overlooked by this technique. I'm still of the opinion that *no*
automated tool can provide complete coverage of an arbitrary web
application, simply because of the potential complexity. It's like solving
the halting problem, to my mind.

Rogan

[1] By "entry point", I mean all onEvent triggers, all "javascript:" hrefs,
etc.

-----Original Message-----
From: RAFAEL SAN MIGUEL CARRASCO [mailto:rsmc () tid es] 
Sent: 24 September 2003 11:11 PM
To: bugtraq () securityfocus com
Subject: Sanctum AppScan 4 misses potential vulnerabilities 
in wrapped links


"AppScan 4.0 Audit Edition, the market leading application 
vulnerability assessment 
tool, accurately detects security vulnerabilities 
automatically as an integrated 
component of an enterprise security process review."

AppScan 4 have a flaw regarding the way the "Explore stage" 
is implemented
when the "Automatic Scan" is selected.
When a reference to a URL in a "a href" tag is made using a 
wrapper function 
instead of directly calling "window.open" or 
"document.location" javascript 
functions, AppScan will not detect the link and the URL will 
not be tested 
against any attack.

As this is a common way to reference URLs (it enables the 
coder to do some 
stuff before the window is actually opened), many pages of a 
website may not
be analyzed by AppScan, hiding potential vulnerabilities to the user. 
An attacker with this knowledge would scan first pages 
referenced in the way 
explained above, speeding up the vulnerability discovery process.

Here is an example of a link that will be ignored by AppScan:

<script>
function openBrWindow(theURL,winName,features) 
{ window.open(theURL,winName,features); }
</script>

<a href="#" onClick="openWindow('bla.html','','');">
<img src="bla.jpg"></a>

I contacted SanctumInc, and this was the solution proposed:

"We are aware of this limitation and in case of extensive 
usage of Java Script 
we recommend the user to choose "Interactive" Scan Type and 
explore the site 
manually. If you do so, just like a normal user will explore 
your site, AppScan 
will test the encapsulated links."

More information about this product: www.sanctuminc.com


Rafael San Miguel Carrasco
División de Infraestructura y Seguridad en Redes IP
Telefónica I+D


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