Name: HTTP PROTOCOL
Version: 1.1
Description: Denies any badly formed HTTP PROTOCOL in the request, 0.9, 1.0, and 1.1 only..
Rules: 
RewriteCond %{THE_REQUEST} !^[A-Z]{3,9}\ .+\ HTTP/(0\.9|1\.0|1\.1) [NC]
RewriteRule .* - [F,NS,L]