A certain algorithm in Ruby on Rails 2.1.0 through 2.2.2, and 2.3.x before 2.3.4, leaks information about the complexity of message-digest signature verification in the cookie store, which might allow remote attackers to forge a digest via multiple attempts.
http://www.vupen.com/english/advisories/2009/2544
http://www.securityfocus.com/bid/37427
http://www.debian.org/security/2011/dsa-2260
http://weblog.rubyonrails.org/2009/9/4/timing-weakness-in-ruby-on-rails
http://secunia.com/advisories/36600
http://lists.opensuse.org/opensuse-security-announce/2009-10/msg00004.html