Cisco IOS XE 3.4 before 3.4.4S 3.5 and 3.6 on 1000 series Aggregation Services Routers (ASR) does not properly implement the Cisco Multicast Leaf Recycle Elimination (MLRE) feature which allows remote attackers to cause a denial of service (card reload) via fragmented IPv6 multicast packets aka Bug ID CSCtz97563.