Securing WordPress Using a Separate, Privileged Apache Vhost

Something I’ve been meaning to check out for a while – locking down WordPress to make it really secure. It’s always freaked me out a bit having web server-writable directories, but it just makes WordPress so powerful and, frankly, easy to use.

I checked out the hardening guide on the official WordPress site. It has a bunch of tips about how to set file system permissions, but at the end of the day you basically need to keep certain directories world-writable if you want to have that handy functionality that lets you do things like install plugins, edit themes, and automatically update.

However, after reading about a new zero-day exploit in a particular file that is packaged with many WordPress themes (not one that I happened to have installed), it drove me to action, along with the realisation that basically none of those simply hardening things is going to be useful if your site is set up with web-writable directories. If there’s an exploit in code – whether it’s core WP code or some random thing you’ve added in a plugin or theme – chances are you’ll be vulnerable.

So I have decided to try something else.

1) I’ve chowned all the files in my WordPress directory to be a non-web user, but left o+rx, which means the web process can happily read everything and serve my files – but it can no longer write to the directory. This of course means all that functionality I mentioned above no longer works.

2) I’ve created a new Apache vhost on my VPS on a separate port. As I am running ITK MTM – a module for Apache that allows me to specify what uid/gid the Apache process will run at on a per-user basis – I can tell this vhost to run as the same username as the non-web user that owns all the files.

3) I’ve made a tiny change to my wp-config.php file so that it lets me access this WordPress instance on the vhost without rewriting the URLs and forwarding me back to the main vhost. I just did something like this:

$t_port = 8958;
$t_servername = '';
if ($_SERVER['SERVER_PORT'] == $t_port)
$t_servername .= ":$t_port";
define('WP_SITEURL', $t_servername);
define('WP_HOME', $t_servername);

4) Now, when I want to perform administrative tasks in WordPress, I just need to remember to access my /wp-admin directory via the vhost.

5) Throw some extra security on this new vhost. I just whapped on a .htaccess in the vhost configuration, but you can do whatever you want – IP restrictions, or whatever.

After doing some basic testing to confirm it was all working as expected, I then went to write this post. I hit ‘save draft’ and was promptly greeted with a bizarre error from my WPSearch plugin (“Fatal error: Call to a member function find() on a non-object in [..]/wp-content/plugins/wpsearch/WPSearch/Drivers/Search/Phplucene.php”). This was mysterious! What had I done wrong?

So I looked through the code and WPSearch and trying to figure out what was going on. Eventually I realised – I’d tried writing this post from my non-privileged vhost. WPSearch must need to write to the disk somewhere as the web user – presumably to update the search index – and it was failing with that error because it wasn’t expecting suddenly to be able to no longer write to the disk (presumably when installing WPSearch it tells you if your file permissions are incorrect for usage).

After that I jumped back in to my privileged vhost and rewrote the post – and so far, so good. I’ll test this for a bit longer but to me it seems like an obvious way of running a more secure instance of WordPress, albeit with a bit more messing around.

Important notes:

Any plugin that you’re running that needs to interact by writing to the disk as part of its usual process will probably fail.

WP Super Cache is one that I’m using that will simply not work with this method – cache requests fail silently from the public interface and the cache simply will not function.

To fix this you need to find out what it needs to write to and give it full permission (which somewhat obviates the point of this exercise, but I’d much rather have only the cache directory world-writable) – in this case, ‘chmod o+w ./wp-content/cache’ fixes up WP Super Cache.

I’ll add more as I discover more.

Updated 2011-08-03: Added WP_HOME into step 3; it is required for various reasons – things like WP Super Cache and the permalinks menu break without it.

Updated 2011-08-15: A new problem – adding images into a post while you’re using the ‘admin port’ means that they’ll get referenced with this port. Not sure how to work around that one.

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