The (1) jdom.rb and (2) rexml.rb components in Active Support in Ruby on Rails before 4.1.11 and 4.2.x before 4.2.2, when JDOM or REXML is enabled, allow remote attackers to cause a denial of service (SystemStackError) via a large XML document depth.
https://groups.google.com/forum/message/raw?msg=rubyonrails-security/bahr2JLnxvk/x4EocXnHPp8J
http://www.securitytracker.com/id/1033755
http://www.securityfocus.com/bid/75234
http://www.debian.org/security/2016/dsa-3464
http://openwall.com/lists/oss-security/2015/06/16/16
http://lists.opensuse.org/opensuse-updates/2015-07/msg00050.html