Cisco Unity 4.x before 4.2(1)ES161, 5.x before 5.0(1)ES53, and 7.x before 7.0(2)ES8, when using anonymous authentication (aka native Unity authentication), allows remote attackers to cause a denial of service (session exhaustion) via a large number of connections.
secunia.com/advisories/32187
securitytracker.com/id?1021013
www.cisco.com/en/US/products/products_security_response09186a0080a0d861.html
www.securityfocus.com/bid/31642
www.voipshield.com/research-details.php?id=128
www.vupen.com/english/advisories/2008/2771
exchange.xforce.ibmcloud.com/vulnerabilities/45743