Telephones are often used without being assigned to a specific user. Some of these telephones, such as those found in printer rooms, can only be accessed by a limited group of people. However, telephones are often found in areas accessible to visitors. These include parking garages or areas near the entrances to access control systems. If these telephones have an electronic telephone book containing internal telephone numbers, these numbers could be exposed to outsiders.

When VoIP telephones are used in freely accessible areas, additional aspects can be relevant. These telephones consist primarily of software and are often operated in data networks that are also used for other IT applications. An attacker could therefore attempt to exploit vulnerabilities in the VoIP software or install malware through direct access to device information.

VoIP telephones need to be connected to a data network. An attacker could connect a mobile IT system to this network and access it under some circumstances, even if it is protected from the outside by a firewall. They could then exploit this access to initiate attacks on confidentiality, integrity, and availability.