Off-by-one error in the encodes function in pack.c in Ruby 1.9.3 and earlier, and 2.x through 2.1.2, when using certain format string specifiers, allows context-dependent attackers to cause a denial of service (segmentation fault) via vectors that trigger a stack-based buffer overflow.
http://www.ubuntu.com/usn/USN-2397-1
http://www.securityfocus.com/bid/68474
http://www.oracle.com/technetwork/topics/security/linuxbulletinjan2016-2867209.html
http://www.debian.org/security/2015/dsa-3157
http://rhn.redhat.com/errata/RHSA-2014-1914.html
http://rhn.redhat.com/errata/RHSA-2014-1913.html