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.
The session fixation protection mechanism in cgi_process.rb in Rails 1.2.4, as used in Ruby on Rails, removes the :cookie_only attribute from the DEFAULT_SESSION_OPTIONS constant, which effectively causes cookie_only to be applied only to the first instantiation of CgiRequest, which allows remote attackers to conduct session fixation attacks. NOTE: this is due to an incomplete fix for CVE-2007-5380.