Ruby (aka CRuby) 1.9 before 1.9.3-p327 and 2.0 before r37575 computes hash values without properly 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, as demonstrated by a universal multicollision attack against a variant of the MurmurHash2 algorithm, a different vulnerability than CVE-2011-4815.
https://www.131002.net/data/talks/appsec12_slides.pdf
https://exchange.xforce.ibmcloud.com/vulnerabilities/79993
https://bugzilla.redhat.com/show_bug.cgi?id=875236
http://www.ubuntu.com/usn/USN-1733-1
http://www.securityfocus.com/bid/56484
http://www.ruby-lang.org/en/news/2012/11/09/ruby19-hashdos-cve-2012-5371/
http://www.ocert.org/advisories/ocert-2012-001.html
http://securitytracker.com/id?1027747