[WeChall] Yourself PHP

Your mission is to inject <script>alert(1);</script> into this script, and make it popup a javascript alert.
The checkit() function tests your injected string for a few static solutions.
Please try to use as less characters as possible and inject the exact same string as above.

Note: This challenge is simulated, and does only check for a few static solutions.
The real XSS flaw got silently fixed, because of security concerns. Thanks noother!
So even if you inject the right code, it will not execute anymore.

GeSHi`ed php code for index.php

<?php
require 'checkit.php'; # required to check your solution/injection
 
chdir('../../'); # chroot to web root
define('GWF_PAGE_TITLE', 'Yourself PHP'); # Wrapper hackrequire_once('challenge/html_head.php'); # output start of website
 
# Get the challenge
if (false === ($chall = WC_Challenge::getByTitle('Yourself PHP'))) {
        $chall = WC_Challenge::dummyChallenge('Yourself PHP', 4, 'challenge/yourself_php/index.php', false);}
# And display the header
$chall->showHeader();
 
# Show mission box (translated)echo GWF_Box::box($chall->lang('mission_i', array('index.php?highlight=christmas')), $chall->lang('mission_t'));
 
# Check your injection and fix the hole by silently applying htmlsepcialchars to the vuln input.
if (phpself_checkit())
{        $chall->onChallengeSolved(GWF_Session::getUserID());
}
 
# Show this file as highlighted sourcecode, if desired
if ('christmas' === Common::getGetString('highlight')){
        $msg = file_get_contents('challenge/yourself_php/index.php');
        $msg = '['.'code=php title=index.php]'.$msg.'['.'/code]';
        echo GWF_Box::box(GWF_Message::display($msg));
} 
 
 
# __This is the challenge:
if (isset($_POST['username'])){
        echo GWF_Box::box(sprintf("Well done %s, you entered your username. But this is <b>not</b> what you need to do.", htmlspecialchars(Common::getPostString('username'))));
}
echo '<div class="box box_c">'.PHP_EOL;
echo sprintf('<form action="%s" method="post">', $_SERVER['PHP_SELF']).PHP_EOL;echo sprintf('<div>%s</div>', GWF_CSRF::hiddenForm('phpself')).PHP_EOL;
echo sprintf('<div>Username:<input type="text" name="username" value="" /></div>').PHP_EOL;
echo sprintf('<div><input type="submit" name="deadcode" value="Submit" /></div>').PHP_EOL;
echo sprintf('</form>').PHP_EOL;
echo '</div>'.PHP_EOL;# __End of challenge
 
 
 
# Print Challenge Footerecho $chall->copyrightFooter();
# Print end of website
require_once('challenge/html_foot.php');
?>