Cisco Unified Communications Manager 4.1 before 4.1(3)SR7, 4.2 before 4.2(3)SR4, 4.3 before 4.3(2), 5.x before 5.1(3), and 6.x before 6.1(1) does not properly validate SIP URLs, which allows remote attackers to cause a denial of service (service interruption) via a SIP INVITE message, aka Bug ID CSCsl22355.