Cisco IOS XR Software Releases 3.3.0 to 4.2.0 contain a vulnerability when handling fragmented packets that could result in a denial of service (DoS) condition of the Cisco CRS Route Processor cards listed in the “Affected Products” section of this advisory.
Read more here – http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20131023-iosxr