The URI.decode_www_form_component method in Ruby before 1.9.2-p330 allows remote attackers to cause a denial of service (catastrophic regular expression backtracking, resource consumption, or application crash) via a crafted string.
https://www.ruby-lang.org/en/news/2014/08/19/ruby-1-9-2-p330-released/
https://github.com/ruby/www.ruby-lang.org/issues/817