Code:
RewriteCond %{QUERY_STRING} base64_encode.*(.*) [OR] 
RewriteCond %{QUERY_STRING} (<|%3C).*script.*(>|%3E) [NC,OR] 
RewriteCond %{QUERY_STRING} GLOBALS(=|[|%[0-9A-Z]{0,2}) [OR] 
RewriteCond %{QUERY_STRING} _REQUEST(=|[|%[0-9A-Z]{0,2}) 
RewriteRule ^(.*)$ index.php [F,L]