As is sadly often the case, well-meaning newcomers to programming take on the newest and/or most popular programming language/framework available. And as you might suspect, they usually get it wrong and make every design and security mistake possible along the way!

This is a trend that we’ve seen with pretty much every popular programming language out there – like for example PHP, which sadly still holds the record for most insecure websites written in the language.

One very popular web framework these days is Ruby on Rails, created by the very talented 29 year old Danish guy David Heinemeier Hansson. It uses a Model-View-Controller construction and emphasizes good design by such principles as DRY (Don’t Repeat Yourself). By all means it’s a very good web framework! But as with PHP, a lot of newcomers get it wrong. Either by not following the Ruby on Rails conventions or by ignoring security!

Now, we’re not here to teach you about design. If you want to learn more about proper software design, a good place to start is simply your local library. Look for books on topics like Design Patterns, Software Engineering, Extreme Programming, Test Driven Development and Agile Software Development.

However what we do want to teach you about, is proper security in Ruby on Rails! Luckily, we don’t have to take out extreme amounts of time from the work we need to do, to get you trained in RoR security – instead we can simply refer to the work already done by the OWASP organization. OWASP is an organization working to improve web application security in the entire world, by means of a whole bunch of different projects for developers, security professionals and end users. One of these projects is the Ruby on Rails Security Guide V2 project which includes a PDF file detailing the different security concerns and solutions concerning Ruby on Rails development.

If you are going to develop Ruby on Rails applications (or if you’re simply curious) please download the Ruby on Rails Security Guide from OWASP and read it before doing any production deployment of applications.

Note: If you’re too busy to go to the project page on OWASP and find the download link, then here’s a direct download link instead: Download the Security Guide

If you’ve ever programmed anything in PHP before, you’ve probably had situations where you needed to be careful with your scripts to make sure they were secure. (and if you haven’t, you probably have but just haven’t noticed)

Making secure code is often times not as easy as you would hope, and while PHP does provide certain methods to help you in your task, it still lets much of the hassle be up to you as the programmer. This construction, combined with the amount of PHP sites out there, leads to the sad fact that many insecure websites are written in PHP. And while your own website may be totally secure, perhaps because you read guides like PHP Security Guide from PHP Security Consortium, there is absolutely no guarantee hosting users on your hosting server will do the same – so you need to protect yourself!

Protecting your server, and more importantly the users on it, is really a matter of several things. You need to make sure only the services you need are running, you need to secure access routes to the server (ssh, vnc, rdp etc.), you need to put in surveillance and detection systems (Nagios, Tripwire, Snort etc.), you need to make sure the data is backed up at all times, you need a proper firewall and tons of other things. Covering all these topics is way beyond this simple post however, so we’ll only focus on protecting yourself against badly coded PHP-scripts.

If a hosting user has a website on your server, say http://www.example.org/, and on this site he creates some PHP script that loads in a file and displays this in some way. Now this is obviously a stupid example, because when would you actually need this functionality? None the less, including files like this is sadly often times done indirectly, making it possible for an attacker to load in arbitrary files and gain full or partial access to the file content. In this example however we’ll simply look at a scheme like the following:

http://www.example.org/script.php?filename=test.txt

Where this script then loads in the content from test.txt.

This kind of setup is very problematic, because an attacker can easily take the request above and change it to load other files like:

http://www.example.org/script.php?filename=../../../../etc/passwd

http://www.example.org/script.php?filename=../../vhosts/someothersite.com/secretfile.php

Where the first one loads the password file on the server (it actually only includes usernames, passwords are in another file – but you get the point) and the second one could be perhaps a configuration file for another hosting user’s blog. This way the attacker could gain access to a complete list of users and some login information for another customer.

Both these situations are obviously unacceptable, and while you can’t protect your users from themselves (at least not easily), you can protect your good users from your more reckless users.

One way of doing this is by utilizing what’s called a chroot. Chrooting basically means taking an application and forcing it to do it’s work solely within a given directory, so that i.e. Apache was only allowed to function inside “/chroot/apache” and nowhere else. This prevents websites running on Apache from reading (and writing) files outside this chroot, so that an attacker can’t use the above attack to read the password file. Setting up such chroots aren’t always that easy, since everything Apache uses during runtime needs to be available in the chroot. One project has however attempted to make chrooting Apache much easier. This project is the Web Application Firewall Mod-Security, which can be found here. They use the so called SecChroot option to easily chroot your Apache.

Chrooting doesn’t however prevent a site in the chroot from reading data in another site stored in the same chroot. To prevent this kind of attack, you’d have to logically separate each running virtual host, by either setting up a dedicated Apache chroot for each virtual host (a bad solution) or use something called suPHP. By means of suPHP, which can be found here, we can make Apache run PHP scripts under the permissions of the owners of the scripts, instead of the normal Apache user which is shared between all virtual hosts. By doing this, we effectively make each virtual host able to only read/write files in its own directory and not spy on other virtual hosts data (assuming these have set correct permissions).

But what if we don’t trust this is enough? What if we want to be completely sure, that even if users set wrong permissions, a given user could still never read or write in another users virtual host? This can be accomplished by means of the php open_basedir option. The open_basedir option can be used to control in which directory the PHP scripts of a virtual host can work. This effectively means we’re actually chrooting the PHP scripts! The way you do this, is that you open up your virtual host configuration (which is probably stored somewhere like “/etc/apache2/vhosts/somevhostcom.conf”) and you then add the following within the <VirtualHost></VirtualHost> pair:

php_admin_value open_basedir /var/chroot/apache/vhosts/somevhost.com

Where “/var/chroot/apache/vhosts/somevhost.com” is the location of the virtual host directory. (be aware: If you’ve chrooted Apache, this path needs to be relative to the chroot and not the actual system).

Using open_basedir is not without it’s problems though. By making the PHP scripts run in what is effectively a chroot, they can’t i.e. write to the /tmp directory, which basically means file uploads won’t work. Be aware that chrooting in general can often lead to these types of issues, which is also why many server administrators just simply choose to take the risk and run Apache without chrooting.

Last but not least you can also use Mod-Security as what it was created as – a Web Application Firewall. A Web Application Firewall is a software firewall placed onto Apache, which then uses a complicated rule set to analyze traffic to the server and identify what kind of traffic is an attack and what is just normal use. These rules however have to be written, at least to some extent, manually and there are issues regarding making rules that catch illegal behavior but never stops legal requests – usually you have to accept some level of false-positives in attack detection if you want to be as secure as you can be.

That’s it! We hope you’ve become a bit more informed now and can get on with making your server secure against bad php scripts. Until next time – Keep safe!

We have now released a native Microsoft Windows installer for the second release of our application Aconiac Password Generator, release 1.2.
It’s available at our website for download, alongside a cross-platform version for Mac, Linux, BSD etc. We are currently working on releasing a bunch of other native installers for Mac, Ubuntu Linux, Redhat/Fedora and more, however with clients needing to be serviced, it might be a few weeks before these will be finished. If you have experience packaging software for these systems and would like to help, please feel free to contact us.

The download page for Aconiac Password Generator can be found here