Directory traversal vulnerability in actionpack/lib/action_dispatch/middleware/static.rb in Action Pack in Ruby on Rails 3.x before 3.2.21, 4.0.x before 4.0.12, 4.1.x before 4.1.8, and 4.2.x before 4.2.0.beta4, when serve_static_assets is enabled, allows remote attackers to determine the existence of files outside the application root via vectors involving a \ (backslash) character, a similar issue to CVE-2014-7818.