| Risk Assessment of telco call acounting | | Print | |
Faced with a steep bill for securing a new SaaS (software as a service) application, a client asked us to help find a way to reduce their risk exposure at the lowest possible cost. By using the Business Threat Modeling methodology and PTA (Practical Threat Analysis) software, we were able to build a risk mitigation plan that mitigated 80% of the total risk exposure in dollars at half the original security budget proposed by the vendor.
AbstractThis paper describes a customer case study of a threat analysis for a next generation call accounting system provided as SaaS, Software as a service . Campton College, a private medical school, needed to replace an aging call accounting system, which frequently lost call records and lacked the capability to provide unified campus-wide telephony billing features. Campton wanted to implement and operate an integrated Web based call accounting system that would service student dorms and administrative departments. The institution contracted with TACS, a call accounting solution provider, to replace the old software and provide a modern, Web-based managed application service that would be cheaper to maintain and easier to use. Prior to implementing the TACS managed call accounting services, Campton retained Software Associates in order to help them perform a risk assessment of the SaaS call accountingsolution. The TACS managed call accounting service in a nutshellTACS offers small to mid-sized organizations a managed software as a service application for call accounting that includes basic billing functionality and is capable of collecting and processing call detail records from variety of sources. The Web-based user interface caters to four different types of users: PBX technicians, administrators, phone users and organization managers. Technicians - TACS technicians are responsible for installing the CDR (call detail records) buffer devices connected to the PBXs for accumulating the calls. A technician defines the parameters of the protocols used by the buffer, data collection schedule, format of call records and performs initial testing of data collection in order to validate that the calls are collected and parsed successfully by TACS data back-end data processing systems. Administrators - Customer administrators handle ongoing management of the telephone switch resources and subscribers as follows:
Subscribers (phone users) - Subscribers can view and print the detailed listings of their private calls and their monthly bills. Managers - User department Managers can produce reports that summarize calls traffic and the usage of telephony resources in the organization. They also monitor the billing and payments of phone users. System ArchitectureThe TACS system ASP architecture is based on Microsoft Windows Server 2003 that runs several .Net applications responsible for the call accounting processing, and a suite of web applications that interact with users via browsers (IE 5.5 and higher). The system database is managed by a stand alone MS SQL 2000 machine connected to the application server via LAN.  DatabaseThe TACS MS SQL Server 2000 stores all types of system data, including call records, pricing programs, users, organizational structure and system configuration. The CDR tables can handle several million records per month and are indexed by a multiple fields to support rich reporting. The SQL Server scheduler mechanism is used to schedule and dispatch the data collection activities. ProcessingThe processing of CDRs has 3 stages: The implementation is based on a several Windows services that use worker components to implement the required functionality. For example, the data collection service operates several different collector components to collect the call records from different data sources via the appropriate protocols. Campton College operates 3 PBXs from different vendors: Avaya, Siemens and a small Cisco VoIP switch. The operating parameters of the components are kept in the database. The data is transferred between the 3 processing stages via MSMQ private queues that serve as non-volatile buffers for data in process. The service processes and some of the worker components were developed using .NET technology. Other worker components are legacy Win32 components wrapped with .NET Interop layer. Web applicationsThe Web Applications are implemented in ASP.NET combined with Microsoft reporting engine. Some of the applications are capable of directly viewing and editing data tables in the database via ASP.NET server side controls. In the TACS system, all Web applications share the same infrastructure for user login and secure access to the database. Pricing, database maintenance and data exchangeThe pricing, database maintenance and data exchange tasks are implemented with a Windows service that uses worker components to perform the actual tasks, similar to the call records processing architecture. The tasks are executed in a periodical manner according to the system schedule. Why conduct a threat analysis?"By retiring an aging 80's in-house system and outsourcing to TACS we will move into the 21st Century in less than nine months; and get an easy to use service that is available to all students and generates a revenue stream,...quot; said Steve Walz, Campton campus operations manager, "but we had security concerns about using an outsourced service."
"We knew that TACS is an experienced call accounting solution provider but we were unsure that their software and operations team had adopted a best-practices approach to information security and we asked TACS to submit to an external assessment of their systems..." said Walz.
What is Business Threat Modeling?A Business Threat Modeling study focuses on protecting valuable assets, is sponsored by a senior manager, has 2-5 participants with relevant knowledge, is guided by an experienced security analyst with specific domain expertis (in this case telecommunications). A typical threat modeling study lasts 2-5 days where the last day is devoted to presenting the results to management. In a pre-kickoff planning meeting, the consultant works with the sponsor to set clearly defined goals and outcomes for the session. Since much of the work is done in small breakout groups, all stakeholders take an active part. The consultant guides the group through a fast-paced process to:
The data collection and risk calculation is performed using PTA Professional. PTA captures the information in a structured database and automates the risk what-if calculation process. Analysts and stakeholders don't need to maintain unstructured Word or Excel documents. Users can quickly create new threat scenarios and countermeasures. All issues are captured and nothing is lost. Management can ask for and quickly receive any reports they want. PTA kickoffAt the first day kickoff session, the functional and architectural descriptions of TACS system were presented to the consultant, by Dympna O'Connell, TACS product manager. "We're already documenting and revising our customer provisioning and configuration procedures", said O'Connell. "We realize that these process steps are crucial to our customer's information security and we want to make sure there are no security holes and opportunities for data manipulation". Step 1 of the study - Identify AssetsIn the first step of the study the group mapped the system's major assets, their financial values and the losses that may be caused when assets are damaged. The following major system assets were identified:
The detailed list of identified assets is part of the full threat-model database available for download from Call Accounting Case Study threat model. To view the detailed entities lists you should have PTA software installed on your computer. Step 2 Identify VulnerabilitiesIn order to identify vulnerabilities and flaws, Open Solutions analysts studied the functional and architecture documents supplied by Ms. O'Connell. "Since TACS bases its architecture on Microsoft infrastructure, we used the PTA MS-Telecom entity library as a base line checklist for picking up system common vulnerabilities" said Yuval, risk consultant. "More then 70% of the stuff was already there. We have just had to complement the picture by diving into the CDR collection equipment and by studying Campton specific business procedures with the help of Mr. Walz.
"Identifying the relevant vulnerabilities is an iterative process bundled with the understanding of the actual threats. All in all, we came up with 15 focused vulnerabilities relevant to the specific architecture, the specific telephony infrastructure and the ASP mode of operation" said Yuval.
Step 3 - Define CountermeasuresDuring this step the team defined the countermeasures relevant for mitigating the identified vulnerabilities. Some of the countermeasures were well known safeguards picked up from the predefined PTA entity library such as enforcing OS patches deployment and strong passwords policy. Others were more unique e.g. the development of mechanism for managing data collection buffer passwords in an encrypted repository.
"We worked directly with Ms. O'Connell and her developers on estimating countermeasures implementation costs needed by PTA for calculating countermeasures cost-effectiveness" said Yuval.
The lists of the 22 countermeasures that were defined and the identified vulnerabilities are included in the case study database available for download from Call Accounting Case Study threat model. Step 4 Build Threat Scenarios
"Building the threats is the peak of the process", said Software Associates founder and CTO Mr. Danny Lieberman, "this is the point where we use our experience to compose the threat scenarios, evaluate their feasibility and estimate the probability they will actually happen".
"The flexibility of the PTA database driven model enables us 'what-if' experiments and the calculative capabilities gives us immediate feedback on the severity of threats" , said Yuval.
Step 5 - Understand the calculated RiskAfter refining threat probabilities, the PTA software calculated the following bottom-line:
The following bar chart presents the 5 most dangerous threats calculated and displayed by PTA (the value of risk is presented in real $): Top Threats by Risk
Not surprising, it was found that the most dangerous threats are the ones that threaten the calls data either in the system database on the various collecting stages.
"The ranking of the threats reflects a typical heterogeneous software system. The ability to take into account non-standard threats specific to the analyzed system is one of the great strengths of PTA ", said Lieberman, "We were not limited to generic information security standards, such as ISO 27001 and indeed you can see some interesting threats that indigenous to this particular system e.g. the CDR buffers vulnerabilities. Complex systems like this often have huge risks that are hidden in the cracks of generic standards..."
Step 6 Optimize CountermeasuresIt was clear that a level of 249% of risk is dangerous and that countermeasures should be applied to reduce the system risk before going into heavy-duty production operation. We asked Open Solutions to show us how to reduce the risk to an acceptable level of 60% at lowest cost, said Steve Walz. Since our budget was constrained, we considered canceling the whole info-sec project and taking our risks by doing nothing. At that step, said Yuval, we ran the PTA optimized risk reduction plan with a target risk level of 50%. We obtained an optimized plan with the following countermeasures that should be applied:
Implementing the recommended set of countermeasures reduces the system risk to 54.3% at a cost of 127,000 $. Only 14 countermeasures out of the 22 were selected - the proposed order of countermeasures also ensures a quickest reduction of risk per $ spent throughout the system modification process. The implementation of the following countermeasures was suspended to later stages in system life cycle:
Steve Walz of Campton College and Ms. O'Connell of TACS summarized their impressions of the study. "We were pleased with the speed and quality of results of the PTA methodology that Open Solutions uses; with the fact that it created consensus among the stakeholders; with the effective use of senior manager time; and above all getting us the best risk reduction at the lowest cost. "
Appendix 1. Abbreviations and terminology
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