Alex Payne

Writer, backer, erstwhile technologist.

Announcing Acts As Sanitized

When I was doing my talk on Rails security at RailsConf Europe I joked about delivering a magical plugin, acts_as_impenetrable, that solved all of your security needs. There’s still no magic bullet for security, but I’d like to contribute a smidge of code that brings us a step closer.

Rails has the ability to mitigate cross-site scripting attacks in the form of its ActionView::Helpers::TextHelpers#sanitize method. This method won’t catch every clever XSS out there, but it sure helps. Sadly, sanitize is unavailable by default from your models and controllers; the expected usage pattern is that you’ll handle sanitization in your view, ex: <%= sanitize(story.title) >@ or <%=h story.body>@.

I don’t think that’s especially, uh, agile (or whatever). Neither is importing those TextHelpers into your controller and reassigning your models’ various attributes to sanitized versions of themselves before saving. It’s tedious, it’s repetitive, and it opens the door to careless errors. Are you sure that you know every field that gets displayed in your views, even after all those revisions and migrations?

My solution to this is a plugin: acts_as_sanitized. You use it like so:

class Comment < ActiveRecord::Base acts_as_sanitized end

That’s it. The plugin figures out which fields in your model are able to be sanitized at application runtime. If you’re not comfortable with that for some strange reason, you can also specify which fields you’d like sanitized. You can even tell it to strip all tags, not just the ones that the sanitize method in Rails handles (script and form). Plus no more monkeying around in your controllers, no more wasteful filtering in your views. Install like so from the root directory of your Rails app:

script/plugin install

Documentation is included in the README file, and there’s a decent suite of tests included.

There isn’t much to this plugin as it stands, but as XSS attacks become ever-more complicated, I’m hoping that this plugin evolves to detect and combat them. If you see attacks that are sneaking by sanitize and strip_tags, let me know! Bugs and patches are more than welcome.