Cisco Unified Communications Manager (Unified CM) 7.1(x) before 7.1(5b)su6a does not properly handle errors, which allows remote attackers to cause a denial of service (service disruption) via malformed registration messages, aka Bug ID CSCuf93466.
http://www.securitytracker.com/id/1028938
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20130821-cucm