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How do SAST, SCA and DAST differ?

What they offer alone, combined and done manually

By Jason Chavarría | August 24, 2022 | Category: Philosophy

Applications make the world go round. Or isn't that the saying? In any case, hardly a day passes without us using some sort of software application. This is why software security is essential. When an application is proven to be insecure, all hell breaks loose

There are different kinds of security tests in the market. This is due to the fact that what the end user sees is just one part of the application, which can be analyzed from different points of view.

In this blog post, we will define the three most popular methods used in software security testing: static application security testing (SAST), software composition analysis (SCA) and dynamic application security testing (DAST). We will see their differences and talk about how they complement each other and, very importantly, how they reach their peak potential when also performed manually by human experts.

What's the difference between SAST, SCA and DAST?

SAST and SCA appear coupled in searches, possibly given that they are both performed looking at the inner contents of the static application and not from the outside while the application is running. Further, DAST and SAST are often pitted against each other. The difference in names (i.e., "static," "dynamic") usually inspires the question "Which one is better?" However, as we will try to convey throughout this post, these methods are performed with different intentions. Therefore any one of them is not necessarily better than the other two. Let's take a look at each of them separately to allow you to see our point.

What is SAST?

Static application security testing (SAST) is a kind of white-box testing. This means that security analysts and tools performing this method have access to source code, byte code or the application's binaries. When people talk about a SAST tool, they mean a program that automatically finds errors in code using sophisticated functions (e.g., data flow analysis, control flow analysis, pattern recognition). It can find them because they coincide with known errors it has stored in a database.

It is not a secret that commercial static application security testing tools generate reports that contain high rates of false positives (lies). This is why human verification is always needed. Experts are responsible for reviewing the results to determine if they are real issues. So, the deployment of these tools should be done along with manual work. Manual SAST is done by security testers who understand the application's context and find security issues in source code that the tool could not flag (i.e., false negatives). A previous blog post explains a little more thoroughly what stages it goes through. The experts are up to date in regards to vulnerabilities thanks to their daily work and contact with resources such as the Open Web Application Security Project (OWASP) and the Common Weakness Ennumeration (CWE). The combination of continuous automatic and manual security testing generates more accurate results.

It's very important to look at the source code performing static application security testing manually alongside automated tools. To give you an idea, our 2022 State of Attacks shows that "Non-encrypted confidential information" and "Sensitive information in source code" are among the top five types of vulnerabilities causing the most risk exposure to the systems Fluid Attacks assessed during 2021.

What are the benefits of SAST?

The following are some of the most notable benefits of static application security testing:

  • It can be done continuously, early and throughout the entire software development lifecycle (SDLC).

  • It allows you to know the exact location of a vulnerability, like the name of the file and line number.

  • As this method informs you of vulnerabilities shortly after they have been written, remediation can take place just as promptly.

  • The earlier you remediate, the more you save on economic costs.

  • When done manually in combination with tools, it yields results with low rates of false positives and false negatives.

What is SCA?

Software composition analysis (SCA) allows you to inventory your open-source components. By knowing their versions, you can check which ones are up to date. And by knowing the component licenses, you can change to other components that do similar stuff but have licenses compatible with your organization's policies in order to prevent legal risk. Further, both manually and aided by tools, SCA points at those components that have vulnerabilities that are listed in public databases or have been disclosed by security testers, researchers or vendors themselves.

Identifying the risk related to vulnerable open-source software dependencies is a top priority. You heard about Log4Shell. How could you not? It is a hot mess to this day. Threat actors keep exploiting vulnerabilities in Log4j because a myriad (perhaps millions, but who knows?) of applications use it for logging. It is still making headlines as people fail to recognize they use it in their software and are therefore exposed to remote code execution and malware attacks, among others.

Log4j is just one of our problems. Our 2022 State of Attacks shows that "Use of software with known vulnerabilities" is the type of vulnerability that generated the most risk exposure and was also present in most systems Fluid Attacks assessed during 2021.

Don't get us wrong, though. We don't think open-source is bad. In fact, we encourage openly sharing your source code, as long as you make sure to test it constantly against vulnerabilities. The importance of open-source security comes, at least partly, from the fact that it makes software development easier. Somewhere around 80% of code in applications comes from open-source dependencies and the rest is proprietary code. The way these libraries are used to be able to create something new fits the standard course of the evolution of human culture. We've said it before: We stand on the shoulders of giants.

What are the benefits of SCA?

The following are among the most remarkable benefits of software composition analysis:

  • It can be done continuously, early and throughout the entire SDLC.

  • It allows you to produce a software bill of materials (SBOM; i.e., a document that states which software dependencies you're using).

  • It helps identify software supply chain risk determined by component quality factors like license, version and vulnerabilities.

  • When done manually in combination with tools, it yields results with low rates of false positives and false negatives.

What is DAST?

Dynamic application security testing (DAST) is a method to assess running applications. That is, these applications are already on a web server, a virtual machine or a container and working. This method does not require access to the source code but rather assesses the application's behavior from the user side, so to speak. As it's done without seeing the source code, it's a type of black-box testing.

Dynamic application security testing involves sending attack vectors (e.g., strings of code) to application endpoints to inspect unexpected behavior. So, for example, if an application does not properly discard unsafe inputs, it is vulnerable to injection attacks (e.g., SQL injection). These attacks may allow criminals to obtain confidential information or achieve remote code execution. So, DAST can help identify these kinds of risks long before the application is even in the hands of end users.

A limitation of dynamic application security testing is that it cannot point to where exactly vulnerabilities reside in source code. Further, as a shared limitation with static application security testing and software composition analysis, when done with tools only, it may produce reports with high rates of false positives (lies) and miss actual vulnerabilities. But the way to overcome false positives and false negatives is combining the use of tools with manual work. When DAST is done manually, the attack surface may be more accurately defined, and the attacks may be specially crafted and up to date on the techniques used by threat actors.

What are the benefits of DAST?

Some of the most notable benefits of dynamic application security testing are the following:

  • It can be done continuously, early and throughout the entire SDLC.

  • It helps identify vulnerabilities that are caused by the interaction with the application.

  • It allows you to simulate attacks by malicious hackers.

  • When done manually in combination with tools, the attacks can be custom made and more clever, yielding results with low rates of false positives and false negatives.

SAST vs SCA vs DAST?

After all these definitions, what could be said about the validity of common comparisons like SAST vs SCA and SAST vs DAST? It's plain to see that these methods are executed with different scopes within the same object of assessment. They each benefit software security in their own way. So, if you ask us whether any one of these methods is better than the other two, we will respond with another question, "What are you intending to do?"

If your answer is something to the effect of "I just wanna know which one will secure my software more effectively," we urge you to snap out of it and think of the importance of comprehensive testing instead. That is, you need to get rid of vulnerabilities in source code, manage your open-source risk and test the application from the stance of an attacker continuously.

Combining SAST, SCA and DAST for comprehensive testing

When you adopt a combined approach to security testing, you are broadening your scope, having a better chance of identifying risk exposure more accurately. Moreover, we urge you to apply these methods continuously across the SDLC, introduce them as soon as possible and combine the manual work with automated testing through it all. The idea is to maintain a strong remediation practice throughout development in which every vulnerability is detected and addressed promptly. The adoption of comprehensive testing will prove to be helpful in building a DevSecOps culture in your organization.

Enjoy Fluid Attacks' comprehensive security testing

At Fluid Attacks, we offer automated and manual SAST, SCA and DAST throughout the entire SDLC, all in a single solution: Continuous Hacking. Our highly certified ethical hackers work continuously alongside tools to detect all the vulnerabilities in the assessed systems. We are constantly expanding the types of vulnerabilities that the tools are able to detect, generating exhaustive reports with minimal false positive rates and boosting our experts' efficiency. In the process, we help you comply with several security standards and reduce remediation costs by up to 90%.

Click here to learn about the 21-day free trial of our Continuous Hacking Machine Plan, which lets you try our automated security testing, or ask us now about our Squad Plan to add ethical hackers to the mix. To learn more, contact us!

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