Probier mal das ersetz es


<?
$_GET['content'] = str_replace('.','',$_GET['content']);
$check = explode("../",$_GET['content']);
if (isset($check[1]) && $check[1]!='') {
echo 'Zugriff verweigert!';
exit;
}
@include_once('lib/header.php');
@include_once('content'.$_GET['content'].'.php');
@include_once('lib/footer.php');
?>