Prevent "Call to undefined function: get_header()" error in theme files

[devonto]

Referencing a ticket from 14 years ago(!) (#1530), I would like to propose that the default WordPress themes - and the theme developer guidelines - be updated to include protection from accessing theme files directly.

Accessing these files give PHP warnings, usually as follows:

Fatal error: Call to undefined function: get_header()

Whilst @markjaquith was correct in stating that theme files are not supposed to be accessed directly, bots are finding their ways into theme folders (and triggering index.php) specifically, resulting in the errors being logged.

I believe it'd be good practice to extend the recommendation from the "Writing a Plugin" documentation (​https://codex.wordpress.org/Writing_a_Plugin#Plugin_Files) to the "Theme Handbook" (​https://developer.wordpress.org/themes/template-files-section/page-template-files/)

Following that recommendation, updating twentynineteen et al to include this (or at least code similar in intention) as the first lines of PHP coding.

defined( 'ABSPATH' ) or die( 'No script kiddies please!' );

[SergeyBiryukov]

Related: #47109

[SergeyBiryukov]

Related: #35835

[SergeyBiryukov]

#47109 was marked as a duplicate.

[SergeyBiryukov]

#53183 was marked as a duplicate.

[SergeyBiryukov]

Hi there, welcome to WordPress Trac!

Thanks for the ticket, sorry it took so long for someone to get back to you.

I think the reason this has not seen any traction yet is because these fatal errors are considered a server configuration issue rather than a security issue per the ​Security FAQ:

Why are there path disclosures when directly loading certain files?
This is a server configuration problem. Never enable display_errors on a production site.

[devonto]

Replying to SergeyBiryukov:

Hi there, welcome to WordPress Trac!

Thanks for the ticket, sorry it took so long for someone to get back to you.

I think the reason this has not seen any traction yet is because these fatal errors are considered a server configuration issue rather than a security issue per the ​Security FAQ:

Why are there path disclosures when directly loading certain files?
This is a server configuration problem. Never enable display_errors on a production site.

Thanks for the update.

I completely agree that errors should not be displayed on a production site, however logging of errors is still good practice.
It is from the server error logs where this is being displayed.

My suggestion is simply to change the recommended setup for PHP files to follow what you have already recommended for plugins.

In addition to triggering index.php files, I often see header.php etc being directly accessed. These are all bot-accessed; so I can only assume they are snooping for vulnerabilities.

Changing the recommendations to include a check if WP is loaded would only serve to improve security.