# Block IP Addresses That Trigger Many 404 Errors

> Temporarily blocks visitors who hit more than 20 missing pages within a minute, a typical sign of vulnerability scanners probing for old plugins and backup files.

- Type: PHP
- Runs: Run everywhere
- Category: [Security](https://wpide.com/library/category/security/)
- Tags: firewall, 404, scanners
- Author: WPIDE Team
- Installs: 0
- Updated: 2026-10-28
- Page: https://wpide.com/library/sec-block-404-scanners/

## Code

```php
// 404 errors allowed per minute, and how long offenders are blocked (minutes).
$wpide_404_limit = 20;
$wpide_404_block = 60;

$wpide_404_key = function () {
    return md5( isset( $_SERVER['REMOTE_ADDR'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REMOTE_ADDR'] ) ) : '' );
};

add_action( 'init', function () use ( $wpide_404_key ) {
    if ( is_admin() || is_user_logged_in() || ( defined( 'WP_CLI' ) && WP_CLI ) ) {
        return;
    }

    if ( get_transient( 'wpide_404_ban_' . $wpide_404_key() ) ) {
        status_header( 403 );
        nocache_headers();
        exit( 'Too many requests for missing pages. Try again later.' );
    }
}, 1 );

add_action( 'template_redirect', function () use ( $wpide_404_key, $wpide_404_limit, $wpide_404_block ) {
    if ( ! is_404() || is_user_logged_in() ) {
        return;
    }

    $key   = 'wpide_404_count_' . $wpide_404_key();
    $count = (int) get_transient( $key ) + 1;
    set_transient( $key, $count, MINUTE_IN_SECONDS );

    if ( $count > $wpide_404_limit ) {
        set_transient( 'wpide_404_ban_' . $wpide_404_key(), 1, $wpide_404_block * MINUTE_IN_SECONDS );
    }
}, 99 );
```

## Notes

Logged-in users are never blocked; raise $wpide_404_limit if you recently changed many URLs and expect lots of broken links.

## How to use it

Install the free WPIDE plugin (https://wordpress.org/plugins/wpide/), find "Block IP Addresses That Trigger Many 404 Errors" in its snippet library and add it in one click; or create a new PHP snippet in WPIDE (or any code snippets plugin) and paste the code above. More snippets: https://wpide.com/library/