Ruby (aka CRuby) before 1.8.7-p357 computes hash values without restricting the ability to trigger hash collisions predictably, which allows context-dependent attackers to cause a denial of service (CPU consumption) via crafted input to an application that maintains a hash table.
https://exchange.xforce.ibmcloud.com/vulnerabilities/72020
http://www.securitytracker.com/id?1026474
http://www.ocert.org/advisories/ocert-2011-003.html
http://www.nruns.com/_downloads/advisory28122011.pdf
http://www.kb.cert.org/vuls/id/903934
http://support.apple.com/kb/HT5281
http://secunia.com/advisories/47822
http://secunia.com/advisories/47405
http://rhn.redhat.com/errata/RHSA-2012-0070.html
http://rhn.redhat.com/errata/RHSA-2012-0069.html
http://lists.apple.com/archives/security-announce/2012/May/msg00001.html
http://jvndb.jvn.jp/ja/contents/2012/JVNDB-2012-000066.html
http://jvn.jp/en/jp/JVN90615481/index.html
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/391606
http://archives.neohapsis.com/archives/bugtraq/2011-12/0181.html