Cisco IOS 15.0 through 15.5 and IOS XE 3.3 through 3.16 allow remote attackers to cause a denial of service (device reload) via a crafted DHCPv6 Relay message, aka Bug ID CSCus55821.
http://www.securitytracker.com/id/1035381
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160323-dhcpv6