How do you balance SAST and DAST in your security testing strategy?

SAST is primarily focused on identifying previously unknown vulnerabilities that are specific to a given application. Rather than searching components known to be vulnerable and comparing them against a database such as the National Vulnerability Database (NVD), SAST tools use heuristics and other logic to identify errors in first-party (i.e. your) code that would not otherwise be detectable by your organization.

SAST (Static Application Security Testing) and DAST (Dynamic Application Security Testing) are complementary tools used to identify security vulnerabilities in web applications. While SAST analyzes the source code, DAST tests the running application.

In my experience, Static Application Security Testing (SAST) is best described as a proactive security measure. It examines the source code, bytecode, or binary code for vulnerabilities before the application runs. SAST is valuable early in the development lifecycle as it identifies security flaws during the coding phase, which is cost-effective and reduces the need for post-deployment fixes. The challenge with SAST, however, lies in the potential for false positives, which can overwhelm developers if not managed correctly. To maximize SAST's potential, integrate it into your CI/CD pipeline and ensure developers receive adequate training on interpreting results.

Dynamic Application Security Testing (DAST) operates on a different principle. It tests the application in its running state, simulating real-world attacks to identify security vulnerabilities in a live environment. DAST is particularly effective at finding issues like runtime vulnerabilities and configuration errors that SAST might miss. One limitation, though, is that it typically requires a running environment and can't pinpoint the exact location in the code where the vulnerability exists. I recommend using DAST as a complementary measure to SAST, especially for testing in pre-production environments to capture runtime security concerns.

SAST and DAST differ fundamentally in their approach and timing within the software development lifecycle. SAST is a white-box testing method, analyzing the application's internal structure without executing the code, making it ideal for early-stage detection. DAST, conversely, is black-box testing, focusing on how the application behaves in a running state to uncover vulnerabilities like injection attacks and cross-site scripting. In practice, the key difference is their vantage point: SAST looks inside-out while DAST tests outside-in. Leveraging both can provide a holistic view of an application's security posture.

SAST (Static Application Security Testing) is a white-box testing method that requires access to the source code for analysis, whereas DAST (Dynamic Application Security Testing) operates as a black-box test, requiring a running application. SAST is typically conducted early in the SDLC, while DAST is applied at later stages. As a result, resolving issues identified by SAST tends to be less costly than addressing those found by DAST. While SAST cannot detect runtime issues, DAST is capable of identifying them.

SAST (Static Application Security Testing) analyzes the source code, detecting vulnerabilities like insecure coding practices before the application runs. It’s proactive and used early in development. DAST (Dynamic Application Security Testing), on the other hand, tests the application from the outside during runtime, identifying vulnerabilities like SQL injection or authentication issues. SAST looks at internal code, while DAST evaluates how the app behaves when deployed and in use.

The primary benefit of SAST is its early detection capabilities. By identifying vulnerabilities during the development phase, SAST helps reduce the cost and complexity of fixing security issues. DAST, on the other hand, shines in identifying vulnerabilities that only appear when the application is live, offering a more realistic assessment of the application's security in its deployed environment. Combining these tools offers a layered security testing approach, ensuring that both code quality and runtime behaviors are scrutinized, thus providing a more comprehensive security strategy.

In a Scaled Agile environment, balancing SAST and DAST is key to maintaining security throughout the continuous delivery pipeline. SAST can be integrated early in the development process during the Continuous Integration (CI) phase, enabling teams to identify and fix vulnerabilities at the code level before features are merged or released. Meanwhile, DAST can be applied during the Continuous Delivery (CD) phase, testing live applications in real-time environments for runtime vulnerabilities. This approach aligns with Agile’s focus on delivering incremental value while ensuring robust security throughout the release cycle.

Striking a balance between SAST and DAST in the Secure Development Lifecycle is key to developing secure products and services. SAST tools can be integrated early into Jenkins jobs during the Continuous Integration (CI) phase, allowing code to be scanned with each check-in on a daily basis. Meanwhile, DAST should be integrated at the deployment stage (CD), identifying vulnerabilities that only surface when the application is running. This combination enables early detection of vulnerabilities through SAST and addresses runtime issues via DAST, maximizing both cost and efficiency benefits.

SAST can produce false positives, which require manual review, leading to increased time and effort. If these rules are ignored across the board, the risk of missing real vulnerabilities becomes significant. On the other hand, DAST requires specialized knowledge to design accurate simulations and effectively integrate them into the pipeline.

In Scaled Agile, SAST and DAST face challenges in iterative cycles. For SAST, false positives slow down teams, and frequent code changes make continuous integration complex. Keeping up with rapid commits demands high tool efficiency and developer training to act on findings. DAST struggles with limited coverage on APIs/microservices and requires stable environments, which Agile’s constant iteration can disrupt. Timing is critical, as DAST can bottleneck rapid feedback loops. Vulnerability identification is tough as rapid changes can reintroduce issues, making it difficult to ensure comprehensive testing across every iteration.

Having an effective and repeatable method for handling SAST and DAST findings is especially crucial and often overlooked. Merely running the scans is one thing. Prioritizing, remediating, and communicating about them is an entirely different thing. Although tools like the Exploit Prediction Scoring System (EPSS) can help with prioritizing CVEs identified in the course of scanning, it is likely you will encounter non-CVEs, especially with SAST. Thus, you need a standardized and quantitative rubric for evaluating their likelihood of malicious exploitation and business impact.

In Scaled Agile, beyond SAST and DAST challenges like false positives and limited API coverage, consider tool scalability as larger codebases and more frequent builds demand higher performance. Ensure seamless CI/CD pipeline integration for automated scans, reducing manual intervention. Address false negatives by fine-tuning rules to prevent missed vulnerabilities. Regular regression testing is critical since continuous code changes may reintroduce known vulnerabilities. Additionally, ensure efficient cross-team communication for rapid dissemination of security findings, especially when multiple teams are working on interconnected systems.

While there are many SAST / DAST tools available, such as SonarQube, Klocwork, Nessus and Burp etc. The real value lies in how effectively these tools are implemented within an organization. Regular updates to the latest versions, periodic reviews of rule exception lists, sprint-based targets for resolving outstanding issues, and seamless integration with Jenkins pipelines are critical factors in maximizing the success of these tools.