In his latest post Padraic Brady talks some about the recent security issues that happened with Ruby on Rails that allowed for remote code execution and how, if you use code blindly, you could be in for a similar fate.
Code execution vulnerabilities are, by definition, hideous monsters. The ability for external inputs to enter an execution context (i.e. injecting or manipulating code that is executed on the server) can be difficult to spot through the haze of convenience that such machinations are often designed to deliver. In Rail’s case, that convenience was to automatically cast data entries in XML or YAML inputs into Ruby types including, unfortunately, Symbols and Objects.
These types of “buried” code execution vulnerabilities are still easy to locate in PHP, at least, because you are still restricted to normal code execution pathways in the absence of Ruby’s dark magic, e.g. eval(), include(), require_once(), system() and, let’s not forget, unserialize().
He talks about how, if you're not careful with the code (third party libraries) that you use in your applications - or don't adhere to good security practices in your own - you could be vulnerable to a similar style of attack. After some investigation on his part, he discovered an issue related to this in the Symfony2 YAML parser (now fixed with a new release).
Pay attention to competing applications or frameworks – their problems may also be your problems. If you’re worried about arbitrary code execution vulnerabilities then audit your code. You can even, as a sanity check, use grep to find uses of functions like eval(), unserialize(), etc and analyse where their parameters’ might originate from.