A vulnerability in the Session Initiation Protocol (SIP) protocol implementation of Cisco Unified Communications Manager could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. The vulnerability is due to insufficient validation of input SIP traffic. An attacker could exploit this vulnerability by sending a malformed SIP packet to an affected Cisco Unified Communications Manager. A successful exploit could allow the attacker to trigger a new registration process on all connected phones, temporarily disrupting service.