active_support/core_ext/hash/conversions.rb in Ruby on Rails before 2.3.15, 3.0.x before 3.0.19, 3.1.x before 3.1.10, and 3.2.x before 3.2.11 does not properly restrict casts of string values, which allows remote attackers to conduct object-injection attacks and execute arbitrary code, or cause a denial of service (memory and CPU consumption) involving nested XML entity references, by leveraging Action Pack support for (1) YAML type conversion or (2) Symbol type conversion.
https://puppet.com/security/cve/cve-2013-0156
https://groups.google.com/group/rubyonrails-security/msg/c1432d0f8c70e89d?dmode=source&output=gplain
http://www.kb.cert.org/vuls/id/628463
http://www.kb.cert.org/vuls/id/380039
http://www.insinuator.net/2013/01/rails-yaml/
http://www.fujitsu.com/global/support/software/security/products-f/sw-sv-rcve-ror201301e.html
http://www.debian.org/security/2013/dsa-2604
http://weblog.rubyonrails.org/2013/1/28/Rails-3-0-20-and-2-3-16-have-been-released/
http://rhn.redhat.com/errata/RHSA-2013-0155.html
http://rhn.redhat.com/errata/RHSA-2013-0154.html
http://rhn.redhat.com/errata/RHSA-2013-0153.html
http://lists.apple.com/archives/security-announce/2013/Mar/msg00002.html