Security threats and data breaches have become more common and can have huge financial and business implications for your organization. As such, you should be able to avoid them by identifying vulnerabilities in your applications and mitigating the risks.

Static application security testing (SAST) and dynamic application security testing (DAST) are two application security testing methods. They are both used to find security vulnerabilities that can make your application susceptible to an attack.

So should you use SAST or DAST? Let’s learn more about these two methods for application security testing and which one should you use.

What is SAST?

Static application security testing (SAST) is a white-box testing method that examines the source code to find software vulnerabilities, flaws, and weaknesses. These vulnerabilities include SQL injection attacks, cross-site scripting, buffer overflows, and others listed in the OWASP Top 10 security risks.

Your team should be performing SAST early and often in the development lifecycle against the entire codebase. SAST tools scan the application from the inside out to identify vulnerabilities in the code before compilation or execution. Since those vulnerabilities are found earlier in the development lifecycle, it makes them easier and faster for developers to fix and enhances the overall application security.

What is DAST?

Dynamic application security testing (DAST) is a black-box testing method that examines an application while it is running to find vulnerabilities that an attacker could exploit. These vulnerabilities include the OWASP Top 10 or the SANS/CWE 25.

Your team should be performing DAST on a running application in an environment similar to production. DAST tools scan the application from the outside in to identify run-time vulnerabilities. Those vulnerabilities are found later in the development lifecycle, making them harder for developers to fix. Remediation often gets pushed into the next cycle, and critical vulnerabilities often need to be fixed as an emergency release.

However, DAST is incredibly useful since it can detect security vulnerabilities that SAST cannot, like those that appear only during the program run-time. Examples include misconfiguration in servers or databases affecting security during run-time and authentication and encryption issues allowing unauthorized access.

What’s the difference between SAST and DAST?

The main differences between the SAST and DAST are where they run in the software development cycle and what kinds of vulnerabilities they find. The following table presents the main differences between SAST and DAST.

SAST	DAST
White-box testing The application is tested from the inside out. The tester has access to the implementation. It represents the developer approach.	Black-box testing The application is tested from the outside in. The tester doesn’t know the implementation. It represents the hacker approach.
Requires source code It analyzes the source code without executing. It does not require a deployed application.	Requires a running application It analyzes by running the application. It does not require source code or binaries.
Finds vulnerabilities earlier in the lifecycle It can be executed as soon as the source code is seen as complete.	Finds vulnerabilities later in the lifecycle It can be executed after the software development cycle is seen as complete.
Less expensive to fix vulnerabilities Vulnerabilities are found earlier in the lifecycle, so it’s easier and faster for developers to fix them.	More expensive to fix vulnerabilities Vulnerabilities are found later in the lifecycle, so it’s harder for developers to fix them.
Can’t find run-time and environment-related issues By scanning static code, it can’t discover run-time vulnerabilities.	Can find run-time and environment-related issues By using dynamic analysis, it can discover run-time vulnerabilities.
Supports all types of software It’s useful for every type of software.	Supports applications and web services only It’s not useful for other types of software.

SAST and DAST: which one should you use?

Now that we covered the main characteristics of SAST and DAST, which one should you use? As we saw before, SAST and DAST are different testing approaches with different benefits, and they complement each other. As such, they are both needed for comprehensively testing your software application and should be used in combination.

A combined approach using SAST and DAST tools will allow you to find a wider range of vulnerabilities and weaknesses that hackers could exploit. Plus, automating SAST and DAST scan with CI/CD allows you to accelerate development time without sacrificing your application’s security.

If you’re looking for a static analysis tool that allows you to check your code quality and keep track of your technical debt, try out Codacy today.