SAST vs. DAST vs. SCA: A Comparison

There are many application security testing (AST) tools on the market. To describe them, we have several acronyms, including SAST, DAST, SCA.

But, what do they mean?

In this post, we’ll cover the similarities and differences between SAST, DAST, and SCA so that you can make an informed decision as to what tool you should use and when in your software development lifecycle.

Static application security testing

Static application security testing (SAST) tools examine code to find software flaws and weaknesses, such as the OWASP Top 10, duplicate code, and hardcoded credentials.

SAST options analyze the application’s source code or binary (this means that most, if not all, SAST tools are language-dependent). They never need to execute the application. Because of this knowledge of an application’s underlying implementation, SAST tools are considered to be a white box method.

Because SAST tools only need the source code or binary, they can be used by developers as soon as they’re ready to push their work to the main branch. This means the security-related issues can be identified early on in the software development life cycle (SDLC) when the cost of fixing such issues is significantly reduced.

There are some downsides to SAST tools, though. They can be noisy, calling attention to issues that may not actually be problematic. If you’re integrating SAST into your SDLC, false positives can result in developers ignoring its alerts (conversely, not finding issues may lead to developers not trusting SAST). Furthermore, some options may be slow due to its testing your product wholly from the inside out.

SAST tools easily support all kinds of software, including web apps and web services, since it doesn’t need to be able to run the application. However, this means that SAST cannot detect runtime vulnerabilities or issues related to the environment in which the application runs.

Dynamic application security testing

Dynamic application security testing (DAST) examines an application as it runs to find flaws and weaknesses that a malicious party could exploit. DAST is considered to be a black-box method since the tools do not know (nor do they need to know) how the application was constructed.

DAST tools do not need access to your application’s source code/binary; they just need to be able to run your application. To get the most out of a DAST option, you should be using it in an environment that matches your production environment as closely as possible. In the end, you’ll find security issues, as well as runtime issues and issues related to your environment.

Because DAST options run the application, you can only use DAST options on applications that can, well, run. This means that you have to be pretty far along in the SDLC before you can test your application. As such, fixing the vulnerabilities identified by a DAST tool can be costly (though one way to minimize such costs can be to release patches for critical vulnerabilities).

While DAST tools aren’t usually language-specific the way that SAST tools are, they’re limited in the types of applications they can test (typically web apps and web services).

SAST v. DAST: which option should you choose?

In the end, SAST and DAST are different testing approaches with different benefits:

They find different types of vulnerabilities

They’re effective in different phases of the software development life cycle

SAST is best performed early and against all source code files

DAST is best performed on a running application in an environment as close to production as possible

If possible, you can use both types of tools to get the best of both worlds!

Software composition analysis

Another common security tool is software composition analysis (SCA), which is a code scanning tool that focuses exclusively on the third-party and open-source components you’re using to build your application.

SCA works by stepping through your source code to create a package bill of materials (BOM). The BOM is a list of packages that are used to help create your applications. Then, it identifies the security vulnerabilities that are introduced due to the inclusion of those packages.

Depending on the SCA tool you choose, you may get additional information, such as whether a vulnerability is attacker-reachable (and therefore a high-priority fix) or if it’s unlikely to present a security issue for your application.

SCA works best at the far left of the SDLC, and in many cases, it is bundled with SAST. As such, any fixes that you might make based on identified open-source vulnerabilities will be cheaper than if they were identified at a later date.

Conclusion

SAST, DAST, and SCA are all commonly used tools in application security. In this article, we’ve covered the high-level similarities and differences between these options and when they might be right for you.