The Skinny Call Control Protocol (SCCP) implementation in Cisco Unified CallManager (CUCM) 3.3 before 3.3(5)SR2a, 4.1 before 4.1(3)SR4, 4.2 before 4.2(3)SR1, and 5.0 before 5.0(4a)SU1 allows remote attackers to cause a denial of service (loss of voice services) by sending crafted packets to the (1) SCCP (2000/tcp) or (2) SCCPS (2443/tcp) port.