How to restrict access to REST API in WordPress

1. Use a plugin to block access to the Rest API (MOST RECOMMENDED WAY)
2. Create a redirect rule in .htaccess configuration to block all requests to the vulnerable URL.
3. Modify source code

Method 1: Using a WordPress plugin,

From experience, we recommend using either Disable REST API or iThemes Security.

Using Disable REST API plugin

1. From within your WordPress dashboard, go to Add Plugin.
2. Search for the plugin called Disable REST API or iThemes Security (or others with good reviews on the same issue)
3. Install and activate the plugin, and that's it

Using iThemes Security plugin

1. From within your WordPress dashboard, go to Add Plugin.
2. Search for the plugin called iThemes Security REST API 
3. Install and activate the plugin
4. In iThemes settings, go to WordPress Tweaks
5. Scroll down to REST API, select the option for Restricted Access. That's it.

WordPress Tweaks

REST API options in iThemes Security settings

iThemes Security is a multi-functional security plugin for WordPress. If you're using to restrict REST API, then consider it's other features to protect your site.

• Disable REST API  - wordpress.org - disable-json-api
• iThemes Security - wordpress.org - better-wp-security

Method 2: Use a redirect rule in the .htaccess configuration file

# BLOCK REQUEST TO WP REST API
# Block/Forbid Requests to: /wp-json/wp/
# WP REST API REQUEST METHODS: GET, POST, PUT, PATCH, DELETE
RewriteCond %{REQUEST_METHOD} ^(GET|POST|PUT|PATCH|DELETE) [NC]
RewriteCond %{REQUEST_URI} ^.*wp-json/wp/ [NC]
RewriteRule ^(.*)$ - [F]

Method 3: Modify source code in WordPress

add_action( 'plugins_loaded', function () {
remove_filter( 'init', '_add_extra_api_post_type_arguments' );
});

add_action( 'plugins_loaded', function () {
remove_filter( 'rest_api_init', 'create_initial_rest_routes' );
});

Alternative code for functions.php file

add_filter( 'rest_authentication_errors', function( $result ) {
    if ( ! empty( $result ) ) {
        return $result;
    }
    if ( ! is_user_logged_in() ) {
        return new WP_Error( 'rest_not_logged_in', 'You are not currently logged in.', array( 'status' => 401 ) );
    }
    return $result;
});

How to verify the REST API is disabled/protected in WordPress

• Visit the following URL replacing example.com with your website's address: **example.com**/?rest_route=/wp/v2/users/1
• You should see a message  in your browser that says something like the following:

{"code":"rest_cannot_access","message":"DRA: Only authenticated users can access the REST API.","data":{"status":401}}

Why disable/protect the REST API in WordPress

Links for additional information on this topic

• digwp - Securing the WP REST API
• stackoverflow.com - Safely disable WP REST API
• wpengine - REST API Vulnerability
• wpsuperstars - A Quick Start Guide To The WordPress REST API

Links for Penetration Testers

• Hackerone - Disclosure of Users Information via WordPress API (?rest_route)
• wpvulndb.com - WordPress 4.7 - User Information Disclosure via REST API