Cisco 9000 Series Aggregation Services Routers (ASR) running Cisco IOS XR Software version 4.1.0 contain a vulnerability that may cause a network processor in a line card to lock up while processing an IP version 4 (IPv4) packet. As a consequence of the network processor lockup, the line card that is processing the offending packet will automatically reload. Cisco has released a free software maintenance upgrade (SMU) to address this vulnerability. There are no workarounds for this vulnerability.