A vulnerability in the Session Initiation Protocol (SIP) UDP throttling process of Cisco Unified Communications Manager (Cisco Unified CM) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to insufficient rate limiting protection. An attacker could exploit this vulnerability by sending the affected device a high rate of SIP messages. An exploit could allow the attacker to cause the device to reload unexpectedly. The device and services will restart automatically. This vulnerability affects Cisco Unified Communications Manager (CallManager) releases prior to the first fixed release; the following list indicates the first minor release that includes the fix for this vulnerability: 10.5.2.14900-16 11.0.1.23900-5 11.5.1.12900-2. Cisco Bug IDs: CSCuz72455.