Name: NO HOST:
Version: 1.1
Description: Denies requests that dont contain a HTTP HOST Header...
Rules: 
RewriteCond %{REQUEST_URI} !^%relative_root%(wp-login.php|wp-admin/|wp-content/plugins/|wp-includes/).* [NC]
RewriteCond %{HTTP_HOST} ^$
RewriteRule .* - [F,NS,L]