Undefined index HTTP_HOST in wp-includes/ms-settings.php on line 57

[JochenT]

We get requests on our server of the form

175.143.12.??? - - [30/Jun/2019:10:22:45 +0200] "GET / HTTP/1.0" 500 73873 "-" "-" (dinse.eu)

This request uses HTTP/1.0 and results in a status code 500. The related entry in the PHP error log is

	[30-Jun-2019 08:22:45 UTC] PHP Notice:  Undefined index: HTTP_HOST in /usr/www/xxxx/wp-includes/ms-settings.php on line 57

1. In ms-settings.php on line 57 it is not checked if

   $_SERVER['HTTP_HOST']
   

   is set.
2. Also I've found that in the case of this specific request

   $_SERVER['SERVER_NAME']
   

   is defined and not empty and can be used as a replacement.

My suggestion is to first check if

$_SERVER['HTTP_HOST']

is set else check if

$_SERVER['SERVER_NAME']

is set and if both are not set to implement a graceful error handling.

This may be related to #34353.

WP 5.2.2
PHP 5.6.40
Server: Apache/2.4.25 (Debian)
WP_DEBUG = true

[JochenT]

Further info:
Apache sets HTTP_HOST to the correspondending value in the ​header of a HTTP request. As mentioned in the doc for the ​UseCanonicalName Directive ancient clients may do not provide a 'Host:...' header.

In such cases SERVER_NAME may be used to construct self-referential URLs. The question is if it still makes sense to support these ancient clients.

Nevertheless, in case HTTP_HOST is missing a convenient error handling should be added.

Trac ticket: https://core.trac.wordpress.org/ticket/47733

A simple patch just to test also the new GitHub environment for contribution :-)

[Mte90]

Patch refreshed :-)

[helen]

Feels a bit late to try this for 5.6 since we're into beta 3 and I worry about unforeseen side effects.

[Mte90]

I see that the code in 2 years isn't changed.

[Mte90]

adding patch also here so I can find the ticket inside trac as contributor

[Mte90]

Any hope for 6.1?

[Mte90]

@SergeyBiryukov there are some chances for 6.2?

[walterebert]

This error also occurs when calling wp-cron.php on the command line.

Tested with WordPress 6.2.2 and PHP 8.2.6.

[Mte90]

Any hope for the next versions?

[SergeyBiryukov]

#63408 was marked as a duplicate.

[SergeyBiryukov]

In 60226:

Bootstrap/Load: Check if HTTP_HOST is defined when determining the current site.

This avoids a PHP warning when running cron via CLI on Multisite:

Warning: Undefined array key "HTTP_HOST" in wp-includes/ms-settings.php on line 62

Follow-up to ​mu:11, ​mu:423, ​mu:543, [12602], [27359].

Props Mte90, JochenT, walterebert, elialum, SergeyBiryukov.
Fixes #47733.