This section describes a typical testing framework that can be developed within an organization. It can be seen as a reference framework that comprises techniques and tasks that are appropriate at various phases of the software development life cycle (SDLC). Companies and project teams can use this model to develop their own testing framework and to scope testing services from vendors. This framework should not be seen as prescriptive, but as a flexible approach that can be extended and molded to fit an organization’s development process and culture.
This section aims to help organizations build a complete strategic testing process, and is not aimed at consultants or contractors who tend to be engaged in more tactical, specific areas of testing.
It is critical to understand why building an end-to-end testing framework is crucial to assessing and improving software security. In ''Writing Secure Code'' Howard and LeBlanc note that issuing a security bulletin costs Microsoft at least $100,000, and it costs their customers collectively far more than that to implement the security patches. They also note that the US government’s CyberCrime web site details recent criminal cases and the loss to organizations. Typical losses far exceed USD $100,000.
With economics like this, it is little wonder why software vendors move from solely performing black box security testing, which can only be performed on applications that have already been developed, to concentrate on testing in the early cycles of application development such as definition, design, and development.
Many security practitioners still see security testing in the realm of penetration testing. As discussed before, while penetration testing has a role to play, it is generally inefficient at finding bugs and relies excessively on the skill of the tester. It should only be considered as an implementation technique, or to raise awareness of production issues. To improve the security of applications, the security quality of the software must be improved. That means testing the security at the definition, design, develop, deploy, and maintenance stages, and not relying on the costly strategy of waiting until code is completely built.
As discussed in the introduction of this document, there are many development methodologies such as the Rational Unified Process, eXtreme and Agile development, and traditional waterfall methodologies. The intent of this guide is to suggest neither a particular development methodology nor provide specific guidance that adheres to any particular methodology. Instead, we are presenting a generic development model, and the reader should follow it according to their company process.
This testing framework consists of the following activities that should take place:
Before application development starts an adequate SDLC must be defined where security is inherent at each stage.
Ensure that there are appropriate policies, standards, and documentation in place. Documentation is extremely important as it gives development teams guidelines and policies that they can follow.
People can only do the right thing if they know what the right thing is.
If the application is to be developed in Java, it is essential that there is a Java secure coding standard. If the application is to use cryptography, it is essential that there is a cryptography standard. No policies or standards can cover every situation that the development team will face. By documenting the common and predictable issues, there will be fewer decisions that need to be made during the development process.
Before development begins, plan the measurement program. By defining criteria that need to be measured, it provides visibility into defects in both the process and product. It is essential to define the metrics before development begins, as there may be a need to modify the process in order to capture the data.
Security requirements define how an application works from a security perspective. It is essential that the security requirements are tested. Testing in this case means testing the assumptions that are made in the requirements and testing to see if there are gaps in the requirements definitions.
For example, if there is a security requirement that states that users must be registered before they can get access to the whitepapers section of a website, does this mean that the user must be registered with the system or should the user be authenticated? Ensure that requirements are as unambiguous as possible.
When looking for requirements gaps, consider looking at security mechanisms such as:
Applications should have a documented design and architecture. This documentation can include models, textual documents, and other similar artifacts. It is essential to test these artifacts to ensure that the design and architecture enforce the appropriate level of security as defined in the requirements.
Identifying security flaws in the design phase is not only one of the most cost-efficient places to identify flaws, but can be one of the most effective places to make changes. For example, if it is identified that the design calls for authorization decisions to be made in multiple places, it may be appropriate to consider a central authorization component. If the application is performing data validation at multiple places, it may be appropriate to develop a central validation framework (ie, fixing input validation in one place, rather than in hundreds of places, is far cheaper).
If weaknesses are discovered, they should be given to the system architect for alternative approaches.
Once the design and architecture is complete, build Unified Modeling Language (UML) models that describe how the application works. In some cases, these may already be available. Use these models to confirm with the systems designers an exact understanding of how the application works. If weaknesses are discovered, they should be given to the system architect for alternative approaches.
Armed with design and architecture reviews and the UML models explaining exactly how the system works, undertake a threat modeling exercise. Develop realistic threat scenarios. Analyze the design and architecture to ensure that these threats have been mitigated, accepted by the business, or assigned to a third party, such as an insurance firm. When identified threats have no mitigation strategies, revisit the design and architecture with the systems architect to modify the design.
Theoretically, development is the implementation of a design. However, in the real world, many design decisions are made during code development. These are often smaller decisions that were either too detailed to be described in the design, or issues where no policy or standard guidance was offered. If the design and architecture were not adequate, the developer will be faced with many decisions. If there were insufficient policies and standards, the developer will be faced with even more decisions.
The security team should perform a code walk through with the developers, and in some cases, the system architects. A code walk through is a high-level walk through of the code where the developers can explain the logic and flow of the implemented code. It allows the code review team to obtain a general understanding of the code, and allows the developers to explain why certain things were developed the way they were.
The purpose is not to perform a code review, but to understand at a high level the flow, the layout, and the structure of the code that makes up the application.
Armed with a good understanding of how the code is structured and why certain things were coded the way they were, the tester can now examine the actual code for security defects.
Static code reviews validate the code against a set of checklists, including:
Having tested the requirements, analyzed the design, and performed code review, it might be assumed that all issues have been caught. Hopefully this is the case, but penetration testing the application after it has been deployed provides a last check to ensure that nothing has been missed.
The application penetration test should include the checking of how the infrastructure was deployed and secured. While the application may be secure, a small aspect of the configuration could still be at a default install stage and vulnerable to exploitation.
There needs to be a process in place which details how the operational side of both the application and infrastructure is managed.
Monthly or quarterly health checks should be performed on both the application and infrastructure to ensure no new security risks have been introduced and that the level of security is still intact.
After every change has been approved and tested in the QA environment and deployed into the production environment, it is vital that the change is checked to ensure that the level of security has not been affected by the change. This should be integrated into the change management process.
The following figure shows a typical SDLC Testing Workflow.