SAST vs DAST: What They Are and When to Use Them

What are SAST and DAST?

When it comes to securing applications, SAST and DAST are two important tools developers rely on to catch vulnerabilities. SAST, or Static Application Security Testing, scans the source code to find issues early in the development process. On the other hand, DAST, or Dynamic Application Security Testing, tests the application in a running state to see how it holds up against real-world attacks.

Using both SAST and DAST together gives teams a more complete picture of an app’s security. SAST catches problems before the code even runs, while DAST shows how the app behaves when it’s live. This combination helps teams build more secure software from start to finish.

What is SAST?

SAST dives deep into the source code without executing it, offering a white-box testing approach. It’s like having an expert reviewer pore over your code, pinpointing areas prone to security breaches such as SQL injections or buffer overflows. By integrating SAST early in the development lifecycle, ideally right after code is committed, developers receive immediate feedback on potential security issues, allowing for swift corrections.

This proactive stance on security ensures that vulnerabilities are addressed long before the code reaches deployment, saving time and resources while fostering a culture of security mindfulness among developers.

What is DAST?

DAST (Dynamic Application Security Testing) takes an external attacker’s perspective, using black-box testing on live web applications to find vulnerabilities such as cross-site scripting and broken authentication. It continuously scans the application during runtime, simulating real-world attacks to detect potential weaknesses. When a vulnerability is identified, DAST alerts the appropriate team to take action.

However, DAST has its limitations. It lacks the ability to provide deep contextual insights into the underlying causes of vulnerabilities, which can make fixing and verifying issues more time-consuming. Because DAST only works with live applications, it’s not suitable for the early stages of the development cycle. The cost of fixing vulnerabilities tends to increase later in the SDLC, making DAST more expensive as issues are discovered later.

Another drawback is that DAST tools rely on signature-based detection, which can lead to false positives and false negatives. False positives waste valuable time and resources as teams manually verify each alert, while false negatives—missed vulnerabilities can result in security breaches or operational disruptions.

Why is SAST important?

SAST is an important way to catch security vulnerabilities early on while the code is still being developed, and long before it’s been deployed. Catching vulnerabilities earlier in the development process typically makes them cheaper and easier to fix. This early detection mechanism not only mitigates the risk of potential security breaches but also aligns with best practices for developing secure applications in today’s fast-paced software development environments.

By prioritizing security from the beginning, teams can significantly reduce the likelihood of costly and damaging security incidents post-deployment, reinforcing the trust users place in the application and the organization behind it. In this way, SAST not only safeguards the application but also upholds the reputation and reliability of the development team, marking a commitment to excellence and trustworthiness in software development.

Why is DAST important?

DAST is valuable for identifying security vulnerabilities that other testing methods might miss, especially those that focus solely on code or internal technologies. By simulating real-world attacks, DAST can pinpoint security weaknesses in your application where an attacker could gain access, allowing you to address them before they’re exploited.

What makes DAST particularly useful is its ability to test applications in their running state. This offers unique insights into how the app behaves in a live environment and highlights vulnerabilities that static analysis might overlook. It’s especially effective for spotting misconfigurations, flaws in authentication and session management, and other operational issues that only arise when the application is running.

Examples of what SAST and DAST can detect

SAST can detect:

• SQL injection
• Buffer overflows
• XML External Entity (XXE) vulnerabilities
• Critical security vulnerabilities identified in industry standards like OWASP Top 10 and SANS/CWE Top 25

DAST can detect:

• Cross-site scripting (XXS)
• SQL injection
• Broken authentication flaws
• Encryption issues
• Misconfigurations of your application server or databases
• Incorrect assumptions about security controls that may not be visible from the source code

What are the main differences between SAST and DAST?

What they scan

SAST scans source code, while DAST scans applications and APIs or web services your application connects to, such as GraphQL, REST, and SOAP.

When they scan

SAST happens early in the software development lifecycle shortly after code is written, while DAST happens later in the development lifecycle once there’s a working application running in a test environment, or even on production code.

Difference in the types of testing

SAST is white-box testing that looks for vulnerabilities inside the application and code, while DAST is black-box testing that looks for vulnerabilities that could allow an outside attacker to get in.

Having access to course code

SAST tools scan the source code of an application, while DAST tools do not have access to source code.

Difference in language dependence

Because SAST is scanning your source code, it’s specific to the programming languages and development frameworks used, and the SAST tool you use needs to support the programming language you are using — whether it’s C++, Python, Go, React, Ruby, or something else.

Unlike SAST, DAST doesn’t care what languages or frameworks your application is built on because it’s testing your application from the outside like an attacker would.

False positives

SAST tends to produce more false positives than DAST. This is because it’s focused on source code and doesn’t have all the context to know if one line of code that looks problematic is actually solved somewhere else. Some DAST providers, such as GitLab, are able to identify some false positives in SAST.

Examples of SAST and DAST TOOLS

Open-source Tools:

• ZED Attack Proxy (ZAP): An open-source tool offered by OWASP for performing security testing on web applications.

Commercial Tools:

Acunetix: An automated web security scanner that accurately scans and audits all types of web applications, including HTML5, JavaScript, and Single Page Applications (SPAs).

• Netsparker: Identifies vulnerabilities in all types of modern web applications, regardless of the underlying architecture or platform.
• InsightAppSec (AppSpider): A comprehensive application security testing solution for the modern web.
• Veracode Dynamic Analysis: Helps companies scan web applications for exploitable vulnerabilities at scale.
• Burp Suite: An integrated platform for web application security testing. It provides tools for mapping, analyzing, and identifying vulnerabilities, from the initial attack surface to exploitation.
• HCL AppScan on Cloud: A DAST tool built as a service that scans both public and privately hosted applications, exploring modern web apps, leveraging recorded steps, and handling complex login scenarios.
• Nuclei: A fast and customizable vulnerability scanner using a simple YAML-based DSL.

Source: https://owasp.org/www-project-devsecops-guideline/latest/02b-Dynamic-Application-Security-Testing

SAST vs DAST?

After understanding the key features and goals of both SAST and DAST testing methodologies, you might be wondering which is the best fit for your application testing process.

The good news is, you don’t have to choose between the two. Using both SAST and DAST together provides a comprehensive approach to security testing, offering continuous feedback at different stages of the development lifecycle.

SAST focuses on analyzing the internal source code early in the development process, helping ensure that developers follow secure coding practices from the start. On the other hand, DAST comes into play later in the development cycle, testing the application while it’s running to identify vulnerabilities related to common cyber threats.

One key difference is that SAST is technology-dependent, meaning the tool you use needs to support the specific programming language and development framework you're working with to ensure thorough coverage. In contrast, DAST is technology-independent since it evaluates the application from an external user’s perspective during runtime.

For the highest level of security in your software, it’s beneficial to integrate both SAST and DAST into your app’s CI/CD pipeline. By combining both approaches, DevSecOps can seamlessly incorporate security into each phase of development. This not only helps to strengthen the application but also allows teams to maintain productivity. Automating both SAST and DAST scans through CI/CD speeds up the development process without compromising the security of the final product.

Summary

SAST and DAST are both essential for comprehensive application security. SAST analyzes source code early in development to ensure secure coding practices, while DAST tests the running application later to identify vulnerabilities from an external attacker’s perspective. Using both tools together in the CI/CD pipeline provides continuous security feedback throughout the development lifecycle, helping teams maintain security without slowing down productivity.

Sources:

• https://owasp.org/www-project-devsecops-guideline/latest/02b-Dynamic-Application-Security-Testing
• https://about.gitlab.com/topics/devsecops/sast-vs-dast/
• https://circleci.com/blog/sast-vs-dast-when-to-use-them/
• https://www.contrastsecurity.com/glossary/devsecops