[CVE-2012-5692] Invision Power Board <= 3.3.4 "unserialize()" PHP Code Execution Vulnerability

[n0b0d13s@xxxxxxxxx]

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Invision Power Board <= 3.3.4 "unserialize()" PHP Code Execution Vulnerability
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author..............: Egidio Romano aka EgiX
mail................: n0b0d13s[at]gmail[dot]com
software link.......: http://www.invisionpower.com/


[-] Vulnerable code in IPSCookie::get() method defined in 
/admin/sources/base/core.php

4015.        static public function get($name)
4016.        {
4017.            // Check internal data first
4018.            if ( isset( self::$_cookiesSet[ $name ] ) )
4019.            {
4020.                return self::$_cookiesSet[ $name ];
4021.            }
4022.            else if ( isset( 
$_COOKIE[ipsRegistry::$settings['cookie_id'].$name] ) )
4023.            {
4024.                $_value = $_COOKIE[ 
ipsRegistry::$settings['cookie_id'].$name ];
4025.    
4026.                if ( substr( $_value, 0, 2 ) == 'a:' )
4027.                {
4028.                    return unserialize( stripslashes( urldecode( $_value ) 
) );
4029.                }

The vulnerability is caused due to this method unserialize user input passed 
through cookies without a proper
sanitization. The only one check is done at line 4026,  where is controlled 
that the serialized string starts
with 'a:',  but this is not  sufficient to prevent a  "PHP Object Injection"  
because an attacker may send  a
serialized string which represents an array of objects.  This can be  exploited 
to execute arbitrary PHP code
via the  "__destruct()" method of the  "dbMain" class,  which calls the 
"writeDebugLog" method to write debug
info into a file.  PHP code may  be injected  only through the  
$_SERVER['QUERY_STRING']  variable,  for this
reason successful exploitation of this vulnerability requires short_open_tag to 
be enabled.


[-] Disclosure timeline:

[21/10/2012] - Vulnerability discovered
[23/10/2012] - Vendor notified
[25/10/2012] - Patch released: 
http://community.invisionpower.com/topic/371625-ipboard-31x-32x-and-33x-security-update
[25/10/2012] - CVE number requested
[29/10/2012] - Assigned CVE-2012-5692
[31/10/2012] - Public disclosure


[-] Proof of concept:

http://www.exploit-db.com/exploits/22398