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Uncaught Error: Call to undefined function wp_kses() with PHP 8.3.6

I migrated my WordPress (multisite) website from PHP 7.4 to PHP 8.3.6 and got the following error:

Fatal error: Uncaught Error: Call to undefined function wp_kses() in /home/devnote/www/wp-includes/functions.php:6073 
Stack trace:
#0 /home/devnote/www/wp-includes/functions.php(5554): wp_trigger_error()
#1 /home/devnote/www/wp-includes/class-wpdb.php(1333): _deprecated_function()
#2 /home/devnote/www/wp-content/sunrise.php(11): wpdb->escape()
#3 /home/devnote/www/wp-includes/ms-settings.php(47): include_once('...')
#4 /home/devnote/www/wp-settings.php(155): require('...')
#5 /home/devnote/www/wp-config.php(107): require_once('...')
#6 /home/devnote/www/wp-load.php(50): require_once('...')
#7 /home/devnote/www/wp-blog-header.php(13): require_once('...')
#8 /home/devnote/www/index.php(17): require('...')
#9 {main} thrown in /home/devnote/www/wp-includes/functions.php on line 6073

./wp-includes/functions.php:

$message = wp_kses(
    $message,
    array(
            'a'      => array( 'href' => true ),
            'br'     => array(),
            'code'   => array(),
            'em'     => array(),
            'strong' => array(),
    ),
    array( 'http', 'https' )
);

Where can this error come from?

I disabled the plugins and changed the theme, see here for details, but it did not help.

WordPress version is 6.7.1 (latest).

After updating to the latest WordPress version 6.7.1 the line numbers changed a little:

Fatal error: Uncaught Error: Call to undefined function wp_kses() in /home/devnote/www/wp-includes/functions.php:6098 Stack trace: 
#0 /home/devnote/www/wp-includes/functions.php(5579): wp_trigger_error()
#1 /home/devnote/www/wp-includes/class-wpdb.php(1333): _deprecated_function()
#2 /home/devnote/www/wp-content/sunrise.php(11): wpdb->escape()
#3 /home/devnote/www/wp-includes/ms-settings.php(47): include_once('...')
#4 /home/devnote/www/wp-settings.php(156): require('...')
#5 /home/devnote/www/wp-config.php(107): require_once('...')
#6 /home/devnote/www/wp-load.php(50): require_once('...')
#7 /home/devnote/www/wp-blog-header.php(13): require_once('...')
#8 /home/devnote/www/index.php(17): require('...')
#9 {main} thrown in /home/devnote/www/wp-includes/functions.php on line 6098

The screenshot of my Multisite Admin panel:

enter image description here

Solution

  • You have an old sunrise.php file left over in the wp-content/ folder.

    It is a drop-in file (compare with Must-Use Plugins and Drop-Ins on my blog).

    And it gets included if the constant named SUNRISE is defined.

    Check your ./wp-config.php file if it is defined there (or otherwise search the string in PHP files) and uncomment the line.

    This then will prevent the drop-in from being loaded and most likely things will work again. If the operations in the file are actually required for your multi-site setup, you have to update the code there in and replace deprecated functionality. But probably it is just an oversight since some version 3 of the installation.