Most security testing strategies begin with scanning application source code or binaries before applications are actually launched. However, no matter how many tests you run against static code, there is always a chance that vulnerabilities will slip past your scans.

That's why Dynamic Application Security Testing, or DAST,  is another essential type of security testing. As this article explains, DAST plays a critical role in identifying security issues that other forms of testing can't uncover.

What is Dynamic Application Security Testing (DAST)?

Dynamic Application Security Testing is the process of checking an application for security vulnerabilities while it's up and running. In other words, DAST allows developers and security analysts to examine how a live application behaves.

Using this approach, engineers can uncover security risks that might not be evident via other forms of security testing – particularly Static Application Security Testing, or SAST, which typically involve scanning static code (meaning source code or non-running binaries), and Software Composition Analysis, or SCA, scans, which check for vulnerable components inside an application.

The role of DAST in the Software Development Lifecycle (SDLC)

DAST scans are usually the last major type of security test that teams perform prior to deploying an application into production. They occur at a later point in the Software Development Lifecycle (SDLC) than SAST scans, which occur when developers write new source code, or when they compile newly written code into binaries (but do not actually deploy the binaries).

Thus, DAST is typically the last opportunity to identify security issues before an application enters a production environment, where any undetected vulnerabilities can be exploited by threat actors. By pairing DAST with SAST and other types of security tests on a unified platform, businesses maximize their ability to detect risks before applications reach the wild.

How do DAST tests work?

To perform DAST tests, engineers typically work through the following steps:

• They set up a testing environment, where they can examine and interact with the application they want to test without exposing it to real-world attacks or disrupting other applications.
• They deploy the application into the test environment.
• Using an automated DAST tool, they simulate actions that threat actors might perform – such as attempting to inject code into application input fields or attempting to escalate user privileges inside the app.
• They evaluate how the application responds to the simulated malicious activity to determine whether it would be vulnerable to similar attacks when deployed in production.

DAST scans can run manually. However, to perform DAST testing at scale as part of continuous software delivery strategies, it's a best practice to automate DAST tests using tools that can set up test environments, deploy applications, and simulate malicious interactions with minimal manual oversight. In addition, tools that automatically analyze and summarize DAST testing results can help teams determine which issues merit their attention, without requiring them to sift through extensive test results by hand.

The importance of DAST scans to application security

The main benefit that DAST brings to application security is its ability to uncover types of risks that would be hard or impossible to detect using other forms of testing.

SAST and SCA tests are effective at catching known risks, such as application modules or dependencies that are associated with vulnerabilities reported in public vulnerability databases. They can also detect some flaws, such as buffer overflow risks or code injection vulnerabilities, that arise from code developers wrote themselves (as opposed to third-party modules or dependencies). They do this primarily by looking for patterns associated with known vulnerabilities or flaws.

However, DAST testing  looks for flaws in a different way – by simulating malicious activities to check whether the application successfully ignores or blocks them. This approach allows DAST todetect security issues that can't be caught by scanning for patterns associated with known types of risks.

DAST vs. SAST, IAST and SCA

If you've read this far, you know that the key differences between DAST and other forms of security testing include:

• Types of risks detected: DAST can detect unknown vulnerabilities or flaws that stem from original source code, whereas SAST and SCA typically look only for known vulnerabilities or common risks.
• Testing methodology: DAST uses a "black box" testing method that scans apps from the outside – the same vantage point that threat actors have. In contrast, SAST and SCA involve "white box" testing that scans applications from the inside, looking at code or binaries that are often never directly exposed to people outside the organization.
• Role in the SDLC: DAST scans usually happen later in the SDLC than SAST and SCA scans. In most cases, DAST is the last major opportunity to catch flaws before applications enter production.
• Testing requirements: DAST requires a live application runtime environment, while SAST and SCA require access only to source code and/or binaries.
• Add a paragraph about the difference vs. IAST (note - IAST is an engine not offered by Checkmarx)

The limitations of DAST

While DAST is an important element of almost any application security strategy, it's important to note that – like other types of security testing – DAST can never guarantee that an application is free of risks and vulnerabilities.

In particular, DAST may not be the best security testing method under conditions like the following:

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• Lack of real-world testing conditions: DAST tests run in testing environments that may not perfectly emulate production, and vulnerabilities may exist in production but not in testing (or vice versa). For example, a production environment may have different access controls in place, or it may include different versions of a software library.
• Inability to test every potential attack: DAST scans usually focus on evaluating common methods of attack. However, because it's impossible to predict every exploit technique that attackers might attempt, there is no way to evaluate every potential risk using DAST.
• Lack of severity assessments: In most cases, DAST tools on their own lack the context necessary to understand the potential severity of risks they uncover. For example, they can determine that part of an application is vulnerable to code injection, but because they don't know what the application is used for or which types of data it handles, they can't predict how much harm the business might suffer if an actual code injection attack occurred.
• Inability to trace root causes: DAST tools can sometimes identify the specific parts of an application that are vulnerable to attack. Yet because they don't scan source code, they can't trace vulnerabilities back to the specific code that needs to be fixed to close the vulnerability. To gain that insight, developers must examine testing reports, and then examine their code base to trace the issue back to the source.

To ensure that you can catch all risks, it's a best practice to deploy other types of tests alongside DAST as part of a comprehensive security strategy.

How to leverage DAST to improve application security

Getting started with DAST is as easy as adding a Dynamic Application Security Testing tool – like Checkmarx DAST – to your set of application security solutions.

With Checkmarx DAST, you can easily scan any live application. In addition, by automatically correlating DAST scan results with SAST scans, Checkmarx DAST can provide the critical context that teams need to prioritize vulnerabilities and plan remediations – a capability that standalone DAST solutions lack. And because Checkmarx DAST integrates seamlessly with popular CI/CD tools, it's easy to make fully automated DAST scans a routine part of your security testing.Learn more by requesting a demo.