SAST vs DAST: What’s the Difference?

SAST and DAST both help to ensure that your software is secure and safeguarded against vulnerabilities. This makes the DevSecOps process easier. Here, we explain the difference between SAST vs DAST to help you better understand when you should use each one.

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SAST vs DAST: Overview of the Key Differences

Both tools are used to identify software security vulnerabilities. However, they work in very different ways. Each method has different benefits and finds different types of vulnerabilities, depending on which stage you are in during software development. Ideally, you will want to have both tools in your security testing toolkit and get to know how best to use them individually and in tandem. 

What Is SAST?

Static Application Security Testing (SAST) typically detects security vulnerabilities early in the software development process and can pinpoint the exact location of these issues and provide details about the severity of the vulnerability. This saves developers a lot of time and headache trying to find and fix issues manually. 

What Is DAST? 

Dynamic Application Security Testing (DAST) usually comes later in the development process to analyze applications in their dynamic (or running) state. This type of testing helps developers to see how the application operates from a user standpoint, with no knowledge of how the software works and the coding insight behind it. DAST tests a wide range of inputs and outputs to dynamically detect vulnerabilities in many different applications as they are running. 

Ideally, SAST and DAST should be used together, so that as many vulnerabilities are covered as possible throughout the software development lifecycle (SDLC). To understand when and how best to apply each testing method, here are the most notable differences between SAST vs DAST.

When to Use SAST vs DAST

Here's what you need to know:

White Box Security Testing
SAST is often referred to as white-box security testing, meaning the developer has access to the underlying framework, design, and implementation of the software. A SAST tool tests the software from the inside out, helping to remove developer bias using industry standards and find issues you may have not considered outside of the predictable failure conditions.

Pre-Code Check-In Check
As part of Continuous Integration (CI) best practices, performing a pre-code check-in before submitting the code allows you to share and receive feedback, as well as continuously test changes earlier in the SDLC. When running a pre-code check-in check within the integrated development environment, a SAST tool helps to automate this process, finding bugs quickly so they are easier to fix, and keeping code quality high. 

Jenkins Pipeline Quality Gate Check
Building a quality gate into your pipeline ensures that important failures do not proceed to the next step before you have a chance to address them. You can add static analysis as part of a quality gate checkmark and use a SAST tool to help you determine quality gate criteria, as well as find errors that contributed to the quality gate failure. 

Nightly Scans
SAST can be performed at all stages of your software development, including server nightly builds. Nightly static analysis scans are a good way to continuously monitor the health of your code, and a more thorough SAST analysis while you're away from your desk identifies vulnerabilities you may have missed, giving you time to fix them when you're actively working. 

Source Code Is Required
This type of tool doesn’t require you to run your software in order to analyze it for vulnerabilities. Instead, it analyzes your source code, byte code, and binaries, without executing anything, generally providing the fastest possible feedback and requiring the least amount of work.

Vulnerabilities Found Earlier in Development and are Less Expensive to Fix
This type of tool is able to scan your code as it is being written. This helps to ensure that security vulnerabilities and coding errors are identified as soon as possible. This also makes it easier, faster, and cheaper to fix those issues.

Unable to Identify Timing- and Environment-Related Issues
As this type of tool scans static code, it is unable to identify timing- and environment-related vulnerabilities.

Generally Supports all Kinds of Software
You can use this type of tool to analyze most types of software, including embedded software, enterprise applications, mobile applications, web applications, and web services.

When to Use DAST vs SAST

Here's what you need to know:

Black Box Security Testing
Conversely, DAST is often referred to as black-box security testing, in which you test the application from the outside in. You don’t have access to the underlying framework, design, and implementation of the software and so internal detail is obscured. This testing approach helps you understand the ways in which a bad actor could find a way in. 

A Running Application Is Required
A DAST tool requires you to run your software in order to analyze it for vulnerabilities.

Vulnerabilities Found Later in Development and are More Expensive to Fix
A DAST tool only analyzes software that can be compiled and run, which means that it can only identify vulnerabilities late in development. This makes it more difficult, time-consuming, and — therefore — more costly to fix errors.

Can Identify Run-Time and Environment-Related Issues
As a DAST tool uses Dynamic Analysis to inspect your software, it is able to identify timing- and environment-related issues.

What are the Advantages of SAST vs DAST?

Here are the main advantages of this type of tool:

• Finds issues by looking for known vulnerability patterns for internationally recognized coding standards for security, as well as safety, and quality.
• Early defect detection and remediation, which lead to lower costs of remediation.
• Shift-Left approach — analysis available everywhere, including developer desktop and CI/CD pipelines.
• Easy to automate, scalable, and automatically provides the highest levels of code coverage.
• Feedback is fast and provides the exact location of vulnerabilities and their cause.

▶️ Related Resource: Read more about the advantages of SAST tools. 

What are the Advantages of DAST vs SAST?

Here are the main advantages of this type of tool:

• Analyzes the whole application as it runs, within the full system environment.
• “Look inside” the application and dynamically analyze execution logic and live data.
• Language and Source Code independent.
• Checks memory consumption and resource use.
• Attempts to break encryption algorithms from outside.
• Verifies permissions to ensure the isolation of privilege levels.
• Checks for cross-site scripting, SQL injection, and cookie manipulation.
• Tests for vulnerabilities in third-party interfaces.
• Understands arguments and function calls.
• Record application execution for post-mortem test failure analysis.
• Catch hard application failures.
• Unattended script-based dynamic analysis.

SAST vs DAST: Use Both SAST and DAST for Your Security Program

As part of an effective security program, both SAST and DAST should be used together, as they are able to identify vulnerabilities that the other may not.

SAST tests the source code early in development. More and more organizations are incorporating SAST testing into both their CI and CD pipelines, so that they can find source code vulnerabilities early and often.

DAST does not have access to the source code, and instead tests the software while it's already running, finding the same security vulnerabilities that a malicious actor may try to exploit. 

However, one testing methodology is not inherently better than the other. Both are needed in order to conduct comprehensive application security testing. Integrating both testing approaches into your pipeline using SAST and DAST automation tools helps to keep your code safe and secure without sacrificing code quality or deliverable timelines. 

For more information on SAST vs DAST, watch our on-demand webinar, Efficient Security Development and Testing Using Dynamic and Static Code Analysis.

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