Cisco Unified Communications Manager (Unified CM) 8.5(x) and 8.6(x) before 8.6(2a)su3 and 9.x before 9.1(1) does not properly restrict the rate of SIP packets, which allows remote attackers to cause a denial of service (memory and CPU consumption, and service disruption) via a flood of UDP packets to port 5060, aka Bug ID CSCub35869.
http://www.securitytracker.com/id/1028938
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20130821-cucm