An Empirical Investigation into the Security of Phone Features in SIP-Based VoIP Systems

Phone features, e.g., 911 call, voicemail, and Do Not Disturb, are critical and necessary for all deployed VoIP systems. In this paper, we empirically investigate the security of these phone features. We have implemented a number of attacks and experimented with VoIP services by leading VoIP service providers Vonage, AT&T and Gizmo. Our experimental results demonstrate that a man-in-the-middle or remote attacker could transparently 1) hijack selected E911 calls and impersonate the Public Safety Answering Point (PSAP); and 2) spoof the voicemail servers of both the caller and the callee of selected VoIP calls; and 3) make spam calls to VoIP subscribers even if Do Not Disturb is enabled. These empirical results confirm that leading deployed SIP-based VoIP systems have serious security vulnerabilities.