Check WordPress Core files integrity

Check WordPress integrity and verify WordPress Core files' md5 checksums against WordPress' checksums API, using this standalone PHP file. I chose to use a standalone PHP script to check the md5sum of WordPress Core files against the API so you're not dependent on a possibly hacked WordPress installation. This kind of guarantees the result can be trusted, as opposed to using a WordPress plugin. I think this is a better integrity check of WordPress Core files.

What do you think of this approach? Let me know through the comments, thanks!

Because it is a standalone PHP script, and not part of WordPress ecosystem, you need to include wp-includes/version.php. Otherwise you are not able to use the $wp_version and $wp_locale variables that are required.

"I trust you", do we trust the WordPress PHP files we have on our systems? Or is the integrity not checked?

Jan Reilink

Calculate SHA-256 checksums in PowerShell

Copy and paste the following code into a new file and upload the file to your WordPress root folder.

<?php
/**
 * Verify WP Core files md5 checksums, outside WordPress.
 * Use this script to verify md5 checksums of WordPress core files.
 * 
 * Follow me on Twitter: @Jan_Reilink
 * Please donate: https://www.paypal.me/jreilink
 */

if ( version_compare( PHP_VERSION, '5.6.29', '<' ) ) {
    die( 'You are using PHP Version: ' . PHP_VERSION . '.
        I think you should use a higher PHP version, at least 5.6.29!
        (change the PHP version check if you must...) ' );
}

/**
 * Put this file in the your WordPress root folder, leave ABSPATH
 * defined  as './'.
 */
define('ABSPATH', './');
if ( defined( 'ABSPATH' ) ) {
    include( ABSPATH . 'wp-includes/version.php' );
    $wp_locale = isset( $wp_local_package ) ? $wp_local_package : 'en_US';
    $apiurl = 'https://api.wordpress.org/core/checksums/1.0/?version=' . $wp_version . '&locale=' .  $wp_locale;
    $json = json_decode ( file_get_contents ( $apiurl ) );
    $checksums = $json->checksums;

    foreach( $checksums as $file => $checksum ) {
        $file_path = ABSPATH . $file;

        if ( file_exists( $file_path ) ) {
            if ( md5_file ($file_path) !== $checksum ) {
                // do something when a checksum doesn't match
                echo "HELP! Checksum for " .$file_path ." does not match!";
            }
        }
    }
}
?>

Now run the file in your browser. No result means everything is OK.

WordPress .htaccess security best practices in Apache 2.4.6+

WordPress file integrity matters and therefore I chose to use a standalone PHP script to check the md5sum of WordPress Core files against the API.

Searching for backdoors in PHP files

When going through a hacked WordPress searching for backdoors, there is not really an advantage in verifying core files checksums first. One might say you don't have to scan files which checksums match, but in my opinion you just have to scan everything.

So if you found this article interesting, you may also like my post using grep to search for backdoors. The post contains a lot of useful grep examples and information, use it wisely.