The decode_credentials method in actionpack/lib/action_controller/metal/http_authentication.rb in Ruby on Rails 3.x before 3.0.16, 3.1.x before 3.1.7, and 3.2.x before 3.2.7 converts Digest Authentication strings to symbols, which allows remote attackers to cause a denial of service by leveraging access to an application that uses a with_http_digest helper method, as demonstrated by the authenticate_or_request_with_http_digest method.