SAST vs. DAST: Which to Choose?

In the world of application security testing, two types of testing reign supreme: DAST and SAST. Both toolings offer extensive benefits to any organization's security stack. Both focus on deeply analyzing source code and application functionalities to diagnose potential security issues accurately.

Unlike security monitoring, DAST and SAST platforms aim to catch any security threats and defects before they can hit production through comprehensive testing. In short, DAST and SAST solutions are about discovery and prevention compared to alternative security approaches that monitor, diagnose, and repair any software flaws while the code is already live.

In this article, we will look at the age-old question of DAST vs SAST by understanding what each solution provides and the key differences in how and when to use them. We will also cover other available tools in the AppSec space that can be paired well with these solutions and provide a holistic approach to application security. With the agenda set, let's get started.

What is Dynamic Application Security Testing (DAST)?

Dynamic application security testing, usually shortened to DAST, is a black box testing method for testing software that involves examining an application while it's running. This “black box” approach to application testing means that the testing tool has no knowledge of the application's internal interactions or design.

A DAST tool simulates attacks against the running application and observes its responses to identify vulnerabilities such as SQL injection or cross-site scripting vulnerabilities. Based on the outcome of each attack, the tool can help to find security vulnerabilities and determine whether the application is vulnerable and could be susceptible to a real malicious attack. These findings allow developers to fix the security defect before the source code is pushed out into the wild.

When should you use DAST?

A DAST tool should be used early on in the Software Development Lifecycle (SDLC). By moving this testing up earlier in the development process, also known as “shifting left”, the security issues can be fixed while active development is happening. A DAST tool can be a great help to all developers and allow them to discover security flaws, coding errors, and defects they've inadvertently put into the code. By nature, DAST tools find issues that are accessible and potentially exploitable, which is great for identifying high-priority items.

Some platforms, such as StackHawk, actually guide developers towards potential fixes for the issue as well, saving developers time. If you're looking to identify runtime vulnerabilities, using a DAST tool is the best approach.

What is Static Application Security Testing (SAST)?

Static application security testing, usually shortened to SAST, is a type of “white box” testing that scans application code statically. SAST tools scan and analyze source code to find source code vulnerabilities by reading through each line of code. When a known vulnerability is identified through static analysis, developers are made aware so that they can remedy the security defect.

SAST tool scans static code of an application before the code is compiled. This also means that source code can be scanned even if it is not in a runnable state, meaning that a SAST solution can be implemented before the first line of code is committed. By doing this, any potential vulnerability that is introduced can be found immediately, versus being detected only once the code is in a runnable state.

What is SAST?

Static application security testing, usually shortened to SAST, is a type of “white box” testing that scans application code statically. SAST tools scan and analyze source code to find security vulnerabilities by reading through each line of code. When a known vulnerability is identified, developers are made aware so that they can remedy the security defect. SAST scans an application before the code is compiled. This also means that code can be scanned even if it is not in a runnable state, meaning that a SAST solution can be implemented before the first line of code is committed. By doing this, any potential vulnerability that is introduced can be found immediately, versus being detected only once the code is in a runnable state.

When should you use SAST?

Like DAST, SAST tools should also be used very early in the development process. Once you find a SAST tool that supports the language you are coding in, it can be moved into the development process. If a project involves writing code, a SAST tool is highly recommended to detect security vulnerabilities at the moment of inception.

Should I use DAST or SAST?

The true answer to whether you should use DAST or SAST is that you should use both, ideally. Both of these testing methodologies provide complementary code coverage and have very different roles when it comes to how they help to secure web and mobile applications further.

There are shortcomings within each platform that can be minimized by overlapping the two technologies. For instance, vulnerabilities found in a third-party API would not be detected by SAST and would require a DAST tool to be accurately identified.

In short, here are a few considerations around what value and concerns each tool can bring to your security testing stack:

• SAST tools are great because they are tied directly to the line of code where the issue is found

• The challenge with SAST is that it can be noisy, flagging lots of issues without clarity around priority or accessibility

• DAST tools are great because they find issues that are accessible to the public internet, inherently baking in prioritization of what should be fixed

• The challenge with DAST is that it does not point to the exact location in the code causing the issue due to it’s black box security testing approach, however this does add the benefit of less false positives

SAST and DAST: better together

Using both SAST and DAST for testing will ensure a more thorough analysis of code from multiple angles, improving code-level security. By integrating both tools, you can provide the benefits of testing runtime behavior and the ability to identify and fix issues in the code.

Other AppSec Tools

Application security tools can be split into two main categories that cover testing and monitoring. Most tools fall somewhere under these categories and both have very different approaches to security. In an ideal world, you will combine both testing and monitoring tools together to create your web application security stack.

Monitoring tools

Monitoring tools are usually used when code has already been deployed into production. Of course, there are cases where monitoring also makes sense to use in lower environments too, such as development or testing environments. Monitoring solutions look for anomalies in a web application traffic, payloads, and other relevant metrics that may indicate a security issue.

Once the monitoring solution detects an issue, it will create an alert for the security or engineering team to check out and fix security issues themselves. The downside to this is that it is a reactive approach to security and less of a preventative one.

On the other hand, application testing tools are a preventative approach that allows potential security defects to be discovered in the code before it gets deployed. SAST and DAST tools are two of the application security testing methods we touched on but they are not the only available testing methods. Many developers also use other types of application security testing tools like IAST and RASP. Let's take a look at some of these two other methods in a bit more detail.

Interactive application security testing (IAST)

Interactive application security testing, shortened to IAST, is a testing methodology that combines the functions of both SAST and DAST. An IAST tool uses a monitoring mechanism, via a sensor or agent, in the application's backend to gather information during runtime.

This approach lets developers test their application's behaviors while the code is running. This part is very much in line with DAST testing techniques. Additionally, the IAST tool also monitors source code execution, like SAST testing.

Runtime application self-protection (RASP)

RASP tools prevent attacks at runtime by analyzing traffic and end-user behavior. When the RASP tool detects an attack, it can issue alerts and block application execution for individual requests. Additionally, some RASP tools can virtually patch the application to fix vulnerabilities and prevent further attacks.

Layering different monitoring and testing tools into your stack is the best way to create secure code and secure applications. By using a variety of tools, you can detect any issues from multiple angles which can help to prevent major security issues from occurring within your web applications and web services.

Wrapping up

Identifying any major or minor security flaw early on in the SDLC is the most efficient and scalable way to increase application security. With the abundance of tools available, adding SAST and DAST tools to your application's security arsenal is a great option. Even better, adding these tools to your organization's SDLC has never been easier, with many even offering deep customization and direct integration with CI/CD pipelines. As you can see, it’s not so much about “SAST vs DAST” but ideally about how to layer the various tools together. Using these platforms is the best way to actively prevent and monitor many of the vulnerabilities and attacks outlined in the OWASP Top Ten. Keeping your applications secure requires multiple angles of prevention and monitoring to ensure a holistic approach to application security.

StackHawk offers a best-in-class DAST tool that is easy to configure and developer-friendly. The platform offers blazingly fast scans right in your CI/CD workflow, and an easy-to-understand report helps developers identify and remedy any security vulnerability that is discovered. To make things even easier, StackHawk easily integrates with Snyk, a popular SAST tool, to offer the best of both worlds by combining results between the two platforms. Ready to up your application security testing game? Sign up for StackHawk today to get started!