Undefined index: HTTP_HOST in wordpress

Question

I am getting in my logs the following error from wordpress: "Undefined index: HTTP_HOST". Of course, the file is requesting $_SERVER['HTTP_HOST'], but how can this be seeing as website is accessed via Apache? I've verified via var_dump that this var exists and is set.

I want to clear this error for my logs and also to find out how this could be possible. I don't have a wordpress CLI cron, so what could this be? I would point out that this is a random request that generated this error. It does not occur when I browse the blog.

Here is the call stack (... = /): Call Stack:

0) 17,
1) ... var... www2... wordpress... wp-blog-header.php 16, 
2) ... var... www2... wordpress... wp-includes... template-loader.php 74, 
3) ... var... www2... wordpress... wp-content... themes... oneengine... page.php 1, 
4) get_header 45, 
5) locate_template 477, 
6) load_template 501, 
7) ... var... www2... wordpress... wp-content... themes... oneengine... header.php 134, 
8) wp_nav_menu 328, 
9) _wp_menu_item_classes_by_context 549

Answer 1

An illegal request might not include it, so it's always possible.

best way to prevent is to check if it exists before using, as with every variable.

<?php
if (array_key_exists('HTTP_HOST', $_SERVER) {
  //use $_SERVER['HTTP_HOST']
}
?>

Or, since it is an illegal request, you could block it.

<?php
if (!array_key_exists('HTTP_HOST', $_SERVER) {
    if (!headers_sent()) {
        $protocol = (isset($_SERVER['SERVER_PROTOCOL']) ? $_SERVER['SERVER_PROTOCOL'] : 'HTTP/1.0');
        header($protocol . ' 404 Not Found');
    }

    echo '<h1>Not Found</h1>';
    exit;
}
?>

Answer 2

It would seem that maybe this is due to a false request. If the client does not send this header, then it does not exist on the server as well, even though it is apache. Must be from script bots.