What is the problem here?
<?php
$template = 'lang.php';
if (isset($_GET['Submit'])) {
$userName = $_GET['userName'];
$userName = stripslashes($userName);
$userName = mysql_real_escape_string($userName);
if (is_numeric($userName)){
$userID = "SELECT userID FROM users WHERE user_name = '$userName'";
$result = mysql_query($userID) or die('<H3>No record or a problem has occurred</H3>');
if (mysql_num_rows($result) > 0){
echo "Welcome $userName";
}}}
if ( is_set( $_COOKIE['languageTemplate'] ) )
$languageTemplate = $_COOKIE['languageTemplate'];
include ( "/tmp/langtemplates/" . $languageTemplate );
?>
-----SPLIT-----
It is a Directory Traversal issue. 'languageTemplate' is not sanitized for file inclusion. 'Cookie: languageTemplate=../../etc/passwd' may return the file content.