Telecommunications Security

Raval • Fichadia John Wiley & Sons, Inc. 2007 Telecommunications Security Chapter Ten Prepared by: Raval, Fichadia

Chapter Ten Objectives • Learn the basic concepts of telecommunications (PSTN, PBX, VoIP) and associated terminology. • Understand the risks that impact telecommunications and the controls to mitigate them. • Gain the skills to assess the security posture of a telecommunications infrastructure and make management recommendations. • Apply security principles and best practices to a telecommunications infrastructure.

The Big Picture Elements of the telecommunications infrastructure. Some risks that impact the infrastructure.

Telecommunication primer Telecommunication: telephone-based communication across different parties using either PSTN or VoIP technologies. • Traditional telephone communication occurs via the Public Switched Telephone Network (PSTN). • PSTN involves transmitting analog voice signals over copper wires to a local station where it is digitized and sent on a dedicated network to its destination end node. • VoIP is newer technology that involves the digitized voice via small packets over shared network. • Vendors that provide PSTN includes AT&T, Qwest. VoIP providers include companies like Vonage.

Telecommunication primer Telecommunication: PSTN components include the following: • End nodes are your basic telephones (for people), modems (for computers), telephony cards (for AVRs). • Phone switches are equipment where a dedicated channel between various callers and receivers is established. • Transmission media typically includes copper wire between end nodes and local phone switch and digital/fiber connections between various switches. • Signaling system that provides call control (connecting / disconnecting callers, determining best route etc.)

Telecommunication primer Telecommunication: Need for phone switches • Connecting phones to every other phone is untenable. For e.g., 10,000 phones need ~50M connections (n*(n-1)/2). • Phone switches solve this problem by acting as a central hub which connects to all phones. 10,000 phones need 10,000 connections (n).

Telecommunication primer Telecommunication: Function of phone switches • Phone switches act as a broker by opening a dedicated circuit when a caller request for it. • Number of circuits are determined by Earlang equations. • Different categories of phone switches: • Private Branch Exchange (PBX): is a privately owned switch • Central Office (CO) is a phone company owned switch that interfaces with end users phones. • Tandem switches: large scale switches that interface to various COs and other tandem switches.

Telecommunication primer Telecommunication: Hierarchy of phone switches • Phones connect to CO switch via local loop. • CO switch connects to tandem switch via trunk lines. • Tandem switches connect to each other.

Telecommunication primer Telecommunication: Transmission media allow a path for user-to-network and network-to-network communication. • User-to-network communication, from home phone to CO, typically occurs over copper wires in an analog format. • Dual-Tone Multiple Frequency (DTMF) is used to signal CO for a communication channel.

Telecommunication primer Telecommunication: Transmission media allow a path for user-to-network and network-to-network communication. • Network-to-network communication, from switch to switch, typically occurs over fiber in a digital format. • Analog signals are digitized via pulse-code modulation (PCM), combined via time-division multiplexing (TDM) and sent over PSTN.

Telecommunication primer Telecommunication: Transmission media allow a path for user-to-network and network-to-network communication. • Over the PSTN tandem switches carry the signal over the network to the destination CO for delivery to the end node.

Telecommunication primer Telecommunication: Signaling system is needed to build a route among switches and to provide call control. • Before a call is sent over the PSTN, a dedicated path (circuit) has to be setup. • Messages to setup a circuit, tear it down, provide busy tones, etc. need to be passed back and forth (call control). • This signaling is accomplished via an out-of-band network called common channel signal (CCS) network. • SS7 is the current implementation of CCS network.

Telecommunication primer Telecommunication: Signaling system is needed to build a route among switches and to provide call control. • SS7 is a packet switched shared network for signaling (PSTN is a circuit switched dedicated network for transmission of voice signals).

Telecommunication primer Telecommunication: VoIP components include the following: • End nodes are VoIP-enabled telephones. They could be like regular phones (hardphones) or be softphones. • Call processors – also known as softswitches – that setup calls, translate phone numbers into IP addresses, do signaling, authorize users, etc. • Media processors that broker transmissions between VoIP and PSTN networks. • Signaling gateways that mediate between signaling on VoIP networks and signaling on PSTN networks.

Telecommunication primer Telecommunication: VoIP networks currently coexist with PSTN networks. • Media processors and signaling gateways bridge the gap between PSTN and VoIP networks.

Telecommunication primer Telecommunication: Advantages of VoIP includes: • Data networks can be reused for voice traffic (convergence). • Enhanced features and functionality compared to PSTN. • Cheaper calls than PSTN networks. Cost doesn’t vary as much by time-of-day or distance. • VoIP allows for location independence – calls follow you. • Allows for efficient use of bandwidth – silence doesn’t consume any bandwidth. • However, quality for VoIP calls still has to catch up with PSTN calls.

Telecommunication primer Telecommunication: Comparison of VoIP vs PSTN:

Management concerns Concerns about telecommunications system security typically include the following: • Maximizing the communication infrastructure availability for employees and customers. • Ensuring the integrity of communications infrastructure. • Keeping up with existing and upcoming telecom scams, toll frauds, social engineering attacks and implementing mitigating controls. • Having an effective backup, recovery, business resumption and a disaster recovery plan.

Risks and controls Remote Access: Feature of PBX that allows long-distance calls to remote users. • Also known as Direct Inward System Access (DISA). • Employees on the road call a toll-free number paid by the company. • The PBX prompts for a passcode and gives a dial tone to make a long-distance call at company’s expense.

Risks and controls Remote access risks: • Phreakers war-dial/dumpster dive/social engineer to identify remote access numbers & crack the passcodes leading to toll-fraud. Controls: • Disable DISA if not reqd. Else, use strong passcodes. • Don’t make 800 #s readily available. • Disable dial tones on DISA ports to foil war-dialers. • Limit places to which long distance calls can be made. • Analyze the logs to identify toll-fraud.

Risks and controls Maintenance ports: Feature of PBX that allows support personnel to administer various features remotely. • Also known as Remote Administration. • Support personnel and vendors call into the PBX and can administer various PBX features. • The PBX prompts for a passcode before allowing access.

Risks and controls Remote access risks: • Phreakers war-dial/dumpster dive/social engineer to identify maintenance port numbers & crack the passcodes leading to toll-fraud, silent monitoring, call rerouting and deny service. Controls: • Disable maintenance ports if not reqd. Else, use strong passcodes or stronger authentication means. • Enable intruder lockouts. • Disable dial tones on DISA ports to foil war-dialers. • Analyze the logs to identify intrusion attempts.

Risks and controls Silent monitoring: Feature of PBX that allows a user to listen in on other’s conversations. • Businesses often have a need to silently listen, record, and/or store conversations among users. • Supervisors listen in on conversations to ensure customer service in a call center/telemarketing type environment. • Sometimes calls are recorded and/or stored for liability or compliance reasons (e.g. air traffic controller).

Risks and controls Silent monitoring risks: • Legal ramifications can arise if calls are monitored without reviewing applicable law. Laws vary by state. • Unauthorized monitoring could occur if administrators aren’t diligent. Controls: • Procure legal consultation before enabling the feature. • Inform callers and employees about the monitoring/ recording practice. Obtain consent forms from latter. • Periodically review the business need for users with the privileges to monitor.

Risks and controls Telecom scams: Several scams usually aimed at toll-fraud, are prevalent within telecom industry. • Shoulder surfing attack includes attackers filming use of calling cards by callers. • Pager/beeper/fax-back scam aims at tricking people calling into expensive toll-numbers. • Operator deceit is a social engineering attempt wherein callers fool company employees to transfer them the operator and asking the operator to make a long-distance call on behalf of the employee. • Employees can misuse call-forwarding feature by forwarding calls to their home numbers and having their friends call the company toll-free number reach them.

Risks and controls Telecom scam risks: • Toll-fraud. Controls: • Educate users about these scams and implement technical controls where possible. • Restrict places to where calls can be made. • Log long-distance activity and analyze logs for abuse. • Limit the call forwarding feature.

Risks and controls Voicemail & conferencing systems: Allows for exchanging message exchanges & conducting conference calls. • Often sensitive information is exchanged via voicemails and/or discussed on conference calls. • Security on these systems is often ignored. Passcodes are almost never changed. Recurring conf calls typically have the same passcodes. • Sometimes these systems allow for zero-out options where the caller can reach an operator – leading to an operator deceit scenario. • “Yes-Yes” scam with mailboxes can lead to third-party billing abuse.

Risks and controls Voicemail & conferencing systems risks: • Poor passcodes can lead disclose sensitive information. • Toll-fraud. Controls: • Ensure strong password & password management. • Educate users and operators about scams. • Disable zero-out and third-party billing options. • Delete unused mailboxes.

Risks and controls VoIP: Technology that involves transmission of digitized voice packets over a shared packet-switched network. • VoIP transmissions are no different that data network transmissions. Hence it suffers from same security issues (see Network security chapter). • VoIP devices are less proprietary in nature (than PSTN devices) and communicate via standard TCP/IP protocols. Hence it is more prone to attacks. • A compromise of data network impacts both computer and telephone traffic. • A compromise of user’s computer could easily impact voice traffic (softphones, web-based voicemail etc.).

Risks and controls VoIP risks: • Sniffing attacks could capture transmissions. • Calls could be hijacked. • DoS attack could disable voice communications. Controls: • Encrypt all VoIP traffic to mitigate sniff risk. • Use Virtual LANs to logically segregate VoIP traffic from the rest of the traffic. • Secure operating systems for PCs and VoIP devices. • Secure networks via firewalls and Intrusion Detection Systems.

Assurance considerations An audit to assess telecommunication security should include the following: • Evaluate the physical security of telecommunications equipment. • Assess the security pass-through/zero-out features available via the PBX, voicemail systems, and conferencing systems. • Review end user education programs to warn them of various telecommunication scams and social engineering attacks. • Ensure that the DISA and maintenance ports are secured against attacks.

Assurance considerations • Review the security all servers that allow for VoIP communications (operating system audit). • Review the security of the network that carries VoIP traffic (network security audit). • Ensure that functional plans for backup and recovery, business resumption, disaster recovery are in place.

Recap

Telecommunications Security