Cisco IOS XR before 4.2.1 on ASR 9000 series devices and CRS series devices allows remote attackers to cause a denial of service (packet transmission outage) via a crafted packet, aka Bug IDs CSCty94537 and CSCtz62593.
http://www.securitytracker.com/id?1027104
http://www.securityfocus.com/bid/53728
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120530-iosxr