Fail2ban Plugin Causing PHP Warnings in Logs

[reneeshgp]

Issue - PHP errors in the debug logs after enabling fail2ban in WordPress. The error is present on all PHP versions above 8.0.

wp-content/plugins/wp-fail2ban/admin/admin.php:304
org\l\c\w\w\admin_menu_fix()
wp-includes/class-wp-hook.php:324
do_action('admin_menu')
wp-admin/includes/menu.php:161

Temporary fix by Adding isset() checks for every array level before accessing the $submenu elements to avoid “undefined array key” warnings. That is to replace: -

    if (isset($submenu['wp-fail2ban-menu']) && 'WP fail2ban' == @$submenu['wp-fail2ban-menu'][0][0]) {
        $submenu['wp-fail2ban-menu'][0][0] = __('Welcome', 'wp-fail2ban');
    }

using the below one in wp-content/plugins/wp-fail2ban/admin/admin.php:304

    // Check if the array key 'wp-fail2ban-menu' exists and has a valid structure
    if (
        isset($submenu['wp-fail2ban-menu']) && 
        isset($submenu['wp-fail2ban-menu'][0]) && 
        isset($submenu['wp-fail2ban-menu'][0][0]) &&
        'WP fail2ban' == $submenu['wp-fail2ban-menu'][0][0]
    ) {
        $submenu['wp-fail2ban-menu'][0][0] = __('Welcome', 'wp-fail2ban');
    }

[wp-fail2ban]

I’d love to know more about what else you’ve got installed as I never managed to reproduce the problem the last time it came up (several years ago now).

Can you try this?

if ('WP fail2ban' == ($submenu['wp-fail2ban-menu'][0][0] ?? '')) {
    $submenu['wp-fail2ban-menu'][0][0] = __('Welcome', 'wp-fail2ban');
}

[reneeshgp]

Hi,

This issue occurs on a default WordPress installation with no other active plugins. During testing, I noticed that the WP Fail2Ban plugin generates PHP errors specifically when interacting with the “Opt-In” option. If I skip the opt-in process, the plugin functions without any issues, but selecting “Opt-In” repeatedly triggers warnings. This indicates that there might be underlying problems with how the plugin handles the opt-in process.

Here are the observations:

1. The “Opt-In” prompt appears right after installing the WP Fail2Ban plugin.
2. Clicking “Opt-In” generates the following PHP errors:

Error Type: Undefined array key and access of a null value.
Location: admin.php file around line 304 in the plugin.

Screenshot is attached for reference.

3. If I click “Skip,” no further errors occur.
4. Once “Allow and Continue” is selected, the opt-in prompt disappears, and the PHP errors stop appearing.

Could you please advise if there is a known fix or if an update is planned to address this issue? Thank you!

[wp-fail2ban]

Thanks for the detailed explanation!

I’ll roll the fix into 5.4 (it’ll be the same as what I posted before).

I know the warning is annoying, but it’s not harmful - everything will work as it should.