The default configuration of Cisco Unity 2.x and 3.x does not block international operator calls in the predefined restriction tables, which could allow authenticated users to place international calls using call forwarding.

Cisco Unity 2.x and 3.x uses well-known default user accounts, which could allow remote attackers to gain access and place arbitrary calls.

Cisco Unity 2.x, 3.x, and 4.x, when integrated with Microsoft Exchange, has several hard coded usernames and passwords, which allows remote attackers to gain unauthorized access and change configuration settings or read outgoing or incoming e-mail messages.

Multiple TCP implementations with Protection Against Wrapped Sequence Numbers (PAWS) with the timestamps option enabled allow remote attackers to cause a denial of service (connection loss) via a spoofed packet with a large timer value, which causes the host to discard later packets because they appear to be too old.