Cisco IOS XR 5.1 allows remote attackers to cause a denial of service (DHCPv6 daemon crash) via a malformed DHCPv6 packet, aka Bug ID CSCuo59052.
https://exchange.xforce.ibmcloud.com/vulnerabilities/95781
http://www.securitytracker.com/id/1030816
http://www.securityfocus.com/bid/69667
http://tools.cisco.com/security/center/viewAlert.x?alertId=35651
http://tools.cisco.com/security/center/content/CiscoSecurityNotice/CVE-2014-3343