Signalingbased Denial of Service







Risk Rating:


At least in theory, VoIP can reduce bandwidth usage and provide quality superior to conventional PSTN. The use of high-bandwidth media common to data communications, combined with the high quality of digitized voice, makes VoIP a powerful and flexible alternative for speech transmission. In practice, however, the process is more complicated. Routing an organization's traffic over a single network can cause congestion and sending it over the Internet can produce a significant delay in the delivery of voice data. Furthermore, the compression techniques used to save bandwidth may slow down the encoding and transmission processes.

As you have already seen, VoIP systems include a variety of other components in addition to traditional end-user equipment: call processors, call managers, gateways, routers, firewalls, and more. Most of these components have counterparts in data networks, but the performance demands of VoIP require the ordinary network software and hardware to be supplemented with special features. One of the main sources of confusion for those new to VoIP is the natural assumption that because digitized voice travels in packets just like other data, existing network architectures and security measures can be used as is. This is simply not true. The unique nature of VoIP services has a significant impact on security considerations and complicates existing networks.

VoIP is a highly demanding technology. It is time-critical and, therefore, a mechanism for assuring that Quality of Service (QoS) meets users' quality expectations is fundamental. The quality associated with VoIP communications has strict parameters, with latency limits at 150 ms and packet loss limits at 3 percent. These stringent limits illustrate VoIP's greatest weakness—high sensitivity to disruptive attacks, commonly known as denial of service (DoS) attacks.

Specifically, the performance requirements and the synergies of the two conflicting natures of a converging network emerge to add new security threats, such as DoS based on signaling protocols. SIP bombing (transmission of a large quantity of bogus SIP

messages to a targeted VoIP system) and fork loops are typical examples of floods usually performed through INVITE messages. Other disruptive attacks include

• CANCEL/BYE abuse (sending of spoofed CANCEL or BYE messages)

• 4XX/5XX/6XX response codes forging (sending spoofed failure messages)

• Exploitation of buffer overflows, format strings, and other programming flaws in protocol implementations

The impact of these attacks on the overall performance of VoIP conversations may ultimately lead to total compromise of the availability requirement of the CIA paradigm (freezing or crashing of VoIP equipment).

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