The DHCPv6 server in Cisco IOS on ASR 9000 devices with software 5.2.0 Base allows remote attackers to cause a denial of service (process reset) via crafted packets, aka Bug ID CSCun72171.
http://www.securitytracker.com/id/1033623
http://tools.cisco.com/security/center/viewAlert.x?alertId=41101