XMLRPC is great for remote publishing to WordPress, but there has been many security issues attributed to it. How do it make it more secure? More specifically, only user from the intranet will be publishing through XMLRPC. WP is currently running on Lighttpd and php5.3.
XMLRPC is as secure as the rest of WordPress. All of the requests need to be authenticated with username and password credentials that exist on your site already. That means, if someone has a login for your site, they can use the XMLRPC interface (if it's turned on). But anonymous users can't get in.
The only potential security vulnerability you might face with XMLRPC is that of a man in the middle attack. But you face this same risk with the regular WordPress admin, so it's not unique to XMLRPC.
The best way to prevent this kind of an issue is to enable SSL security on your site. You'll need an SSL certificate, and then you need to access you XMLRPC endpoint via
https:// rather than
http://. This will encrypt your requests and prevent anyone from intercepting them and stealing your credentials.
You should also enable SSL security on login for your regular site because it, too, faces the same risks.
To limit access to xmlrpc.php to only the IP range that needs it (e.g. Jetpack) you can do something like this.
<files xmlrpc.php=""> Order Deny,Allow Deny from all Allow from 220.127.116.11/18 Satisfy All ErrorDocument 403 http://127.0.0.1/ </files>
Securing xmlrpc.php seems generally under-discussed on the web but an attack can mean a DoS attack. Definitely worth discussing to make sure more people can prevent an attack, in my opinion.
The plugin Secure XML-RPC seems to address the issue of sending sensitive info over the wire.
Rather than sending usernames and passwords in plain text with every request, we're going to use a set of public/secret keys to hash data and authenticate instead.