The DHCPv6 implementation in Cisco IOS XR allows remote attackers to cause a denial of service (device crash) via a malformed packet, aka Bug IDs CSCum85558, CSCum20949, CSCul61849, and CSCul71149.
http://www.securitytracker.com/id/1030259
http://tools.cisco.com/security/center/content/CiscoSecurityNotice/CVE-2014-3271