Cisco IOS 15.5(3)S3, 15.6(1)S2, 15.6(2)S1, and 15.6(2)T1 does not properly dequeue invalid NTP packets, which allows remote attackers to cause a denial of service (interface wedge) by sending many crafted NTP packets, aka Bug ID CSCva35619.
http://www.securitytracker.com/id/1036541
http://www.securityfocus.com/bid/92317
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160804-wedge