actionpack/lib/action_dispatch/http/request.rb in Ruby on Rails before 3.2.16 and 4.x before 4.0.2 does not properly consider differences in parameter handling between the Active Record component and the JSON implementation, which allows remote attackers to bypass intended database-query restrictions and perform NULL checks or trigger missing WHERE clauses via a crafted request that leverages (1) third-party Rack middleware or (2) custom Rack middleware.  NOTE: this vulnerability exists because of an incomplete fix for CVE-2013-0155.