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.
http://www.vupen.com/english/advisories/2007/4238
http://www.vupen.com/english/advisories/2007/4009
http://www.us-cert.gov/cas/techalerts/TA07-352A.html
http://www.securityfocus.com/bid/26598
http://weblog.rubyonrails.org/2007/11/24/ruby-on-rails-1-2-6-security-and-maintenance-release
http://secunia.com/advisories/28136
http://secunia.com/advisories/27781
http://lists.apple.com/archives/security-announce/2007/Dec/msg00002.html
http://docs.info.apple.com/article.html?artnum=307179