Threat Assessment focuses on identifying threats in applications.
The Threat Assessment (TA) practice focuses on accurately identifying and understanding potential attacks upon an organisation’s software to better understand the risks and facilitate risk management. Indeed, software assurance is all about identifying risks in applications and treating them accordingly.
Risks to an application can be relative to the business of the application (think about business logic attacks) or to the technical setup of the application. The Application Risk Profile stream deals with the former, while the Threat Modeling focuses on the latter.
|A: Application Risk Profile||B: Threat Modeling|
|Maturity 1 - Best-effort identification of high-level threats to the organization and individual projects.||Basic assessment of the application risk||Best effort ad-hoc threat modeling|
|Maturity 2 - Standardization and enterprise-wide analysis of software-related threats within the organisation||Understand the risk for all applications in the organisation||Standardized threat modeling|
|Maturity 3 - Pro-active improvement of threat coverage throughout the organisation||Periodicly review application risk profiles||Improve quality by automated analysis|
A: Application Risk Profile
Ability to classify applications according to risk
As an organisation, you want to spend your security budget where it matters. Application risk is a good tool to guide your security spending. A risk classification helps identify which applications can pose a serious threat to the organisation if they were attacked or breached.
Use a simple method to evaluate the application risk per application, estimating the potential business impact that it poses for the organisation in case of an attack. To achieve this, evaluate the impact of a breach in the confidentiality, integrity and availability of the data or service. Consider using a set of 5-10 questions to understand important application characteristics, such as whether the application processes financial data, whether it is internet facing, or whether privacy-related data is involved. The application risk profile tells you whether these factors are applicable and if they could significatly impact the organisation.
Next, use a scheme to classify applications according to this risk. A simple, qualitative scheme (e.g. high/medium/low) that translates these characteristics into a value is often effective. It is important to use these values to represent and compare the risk of different applications against each other. Mature highly risk-driven organisations might make use of more quantitative risk schemes. Don’t invent a new risk scheme if your organisation already has one that works well.
Evaluate the risk based on the set of questions and assign a risk level to each application.
Solid understanding of the risk level of an application
The goal of this activity is to thoroughly understand the risk level of all applications within the organisations to focus the effort of your software assurance activities where it really matters.
From a risk evaluation perspective, the basic set of questions is not enough to thoroughly evaluate the risk of all applications. Create an extensive and standardized way to evaluate the risk of the application, among others via their impact on information security (confidentiality, integrity and availability of data). Next to security, you also want to evaluate the privacy risk of the application. Understand the data that the application processes and what potential privacy violations are relevant. Finally, study the impact that this application has on other applications within the organisation (e.g., the application might be modifying data that was considered read-only in another context). Evaluate all applications within the organisation, including all existing and legacy ones.
Consider using quantitative schemes to classify application risk. A simple qualitative scheme (such as high/medium/low) is not enough to effectively manage and compare applications on an enterprise-wide level.
Based on this input, build a centralized inventory of risk profiles that use the outcome of the risk evaluations to define the profile. This inventory gives all stakeholders an aligned view of the risk level of an application to assign appropriate priority to security-related activities.
Timely update of the application classification in case of changes
The application portfolio of an organisation changes, as well as the conditions and constraints in which an application lives (e.g., driven by the company strategy). Periodically review the risk inventory to ensure correctness of the risk evaluations of the different applications.
Have a periodic review at an enterprise-wide level. Also, as your enterprise matures in software assurance, stimulate teams to continuously question which changes in conditions might impact the risk profile. For instance, an internal application might become exposed to the internet by a business decision. This should trigger the teams to rerun the risk evaluation and update the application risk profile accordingly.
In a mature implementation of this practice, train and continuously update teams on lessons learned and best practices from these risk evaluations. This leads to a better execution and a more accurate representation of the application risk profile.
B: Threat Modeling
Basic understanding of potential threats to the solution
The purpose of Threat Modeling is to pro-actively identify potential issues in the technical design of the application. A careless setup might lead to important attack vectors in an application that can be exploited to target your organisation. Experience shows that architectural design can be an important source of security issues, and the consequences can be significant.
The practice of threat modelling includes both eliciting and managing threats. Use known good security practices (or the lack thereof) or a more structured approach such as STRIDE to elicit threats. Threat modelling is often most effective when performed by a group of people, allowing for brainstorming. One of the key challenges in threat modelling is working towards a list of relevant and important threats in an efficient exercise, and avoiding lengthy processes and overly detailed lists of low-relevant threats. Experience helps find a proper balance.
Perform threat modeling iteratively to align to more iterative development paradigms. If you add new functionality to an existing application, look only into the newly added functions instead of trying to cover the entire scope.
Execute threat modeling on important projects (LINK: Application Risk Profile) in a best effort mode to identify the most important threats to the application. Existing network diagrams you can annotate during discussion workshops are a good starting point.
Improved elicitation and management of threats to the solution
Establish a standard approach to perform structured threat modeling to increase the quality and efficiency of threat modeling within your organisation, and ensure that the invested effort is useful and well spent. Structured threat modeling takes into account the different actors, assets and flows to identify an extensive list of potential threats to the application. It defines the inputs required to start the activity (e.g., a technical architecture overview and a data flow diagram), the different steps to identify threats, and the formalisms to describe or annotate the threats. You can add mitigating controls to threat models to guide designers in dealing with particular threats.
As an organisation, define what triggers the execution of threat modeling. For example a change in architecture, or a deployment of an application in a new environment. At the same time, think about ways to support scaling of threat modeling throughout the organisation.
Feed the output of threat modeling to the defect management process for adequate follow-up. Adopt a weighting system to measure and compare the importance of the different threats.
Consider using a tool to manage the treat models of the different applications. Train people to focus on important threats as one of the challenges in threat modeling is a potential overload of trivial threats. Tools help in identifying potential threats but, in the end, threat modeling requires human intelligence that cannot be easily automated.
Timely update and qualitative management of application threat
In a mature setup of threat modeling, regularly (e.g., yearly) review the existing threat models to verify that no new threats are relevant for your applications.
Use automated analysis to evaluate the quality and discover gaps and/or patterns in the threat models. These can improve the threat models.
Review the threat categories relevant to your organisation. When you identify new threat categories, feed this information to the organisation to ensure appropriate handling.