300 Chapter 12 It must be noted that it is not difficult for unscrupulous elements to break into the cellular network and cause outages. The major reason for this is that cellular networks were not designed with security in mind. They evolved from the old-fashioned telephone networks that were built for performance. To this day, the cellular network has numerous well-known and unsecured vulnerabilities providing access to adversaries. Another feature of cellular networks is network relationships (also called dependencies) that cause certain types of errors to propagate to other network locations as a result of regular network activity. Such propagation can be very disruptive to the network, and in turn it can affect subscribers. Finally, Internet connectivity to the cellular network is another major contributor to the cellular network's vulnerability because it gives Internet users direct access to cellular network vulnerabilities from their homes. To ensure that adversaries do not access the network and cause breakdowns, a high level of security must be maintained in the cellular network. However, though great efforts have been made to improve the cellular network in terms of support for new and innovative services, greater number of subscribers, higher speed, and larger bandwidth, very little has been done to update the security of the cellular network. Accordingly, these networks have become highly attractive targets to adversaries, not only because of their lack of security but also due to the ease with which these networks can be exploited to affect millions of subscribers. In this chapter we analyze the security of cellular networks. Toward understanding the security issues in cellular networks, the rest of the chapter is organized as follows. We present a comprehensive overview of cellular networks with a goal of providing a fundamental understanding of their functioning. Next we present the current state of cellular network security through an in-depth discussion on cellular network vulnerabilities and possible attacks. In addition, we present the cellular network specific attack taxonomy. Finally, we present a review of current cellular network vulnerability assessment techniques and conclude with a discussion. 2. Overview of Cellular Networks The current cellular network is an evolution of the early-generation cellular networks that were built for optimal performance. These early-generation cellular networks were proprietary and owned by reputable organizations. They were considered secure due to their proprietary ownership and their closed nature, that is, their control infrastructure was unconnected to any public network (such as the Internet) to which end subscribers had direct access. Security was a nonissue in the design of these networks. Recently, connecting the Internet to the cellular network has not only imported the Internet vulnerabilities to the cellular network, it has also given end subscribers direct access to the control infrastructure of the cellular network, thereby opening the network. Also, with the www.syngress.com