WEBrick is an HTTP server library written in Ruby that uses servlets to extend its capabilities. Built into WEBrick are four servlets, handling CGI, ERb, file directories, and a generic Proc servlet. Ruby on Rails uses WEBrick as a quick and easy webserver to start developing your Rails applications. However, for whatever ease of development WEBrick adds to your application, it is generally considered not suitable for any production environment. The Ruby WEBrick HTTPd server has been found to contain a directory traversal security vulnerability.
http://www.securiteam.com/securitynews/5TP0F1PNQK.html
