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SAST vs. DAST: 5 Key Differences and Why to Use Them Together

September 27, 2023
Edward Chopskie

What Is SAST (Static Application Security Testing)? 

SAST, or Static Application Security Testing, is a type of security testing that examines the application’s source code at a static, or non-running, state. This method of testing is often referred to as “white box” testing because it provides a comprehensive view of the application’s code, allowing for a thorough examination of potential vulnerabilities.

SAST is typically performed early in the development lifecycle, often even before the code is executed. The primary aim of SAST is to identify vulnerabilities and flaws in the software’s code that could potentially lead to security breaches. By reviewing the code in its non-running state, SAST can help identify issues like input validation errors, buffer overflows, and insecure server configurations.

While SAST is a powerful tool for identifying potential security issues, it’s not without its challenges. The static nature of SAST means it can’t identify runtime vulnerabilities, and it can sometimes produce false positives. However, when used correctly and in conjunction with other testing methods, SAST can be a valuable part of a comprehensive security strategy.

What Is DAST (Dynamic Application Security Testing)? 

Dynamic Application Security Testing (DAST), on the other hand, is a “black box” testing methodology. This means that unlike SAST, DAST doesn’t require access to the application’s source code. Instead, DAST tests the application in its running state, simulating the actions of an attacker to identify potential vulnerabilities.

DAST is typically performed later in the development cycle, often just before deployment. It aims to identify vulnerabilities that may not be evident in the source code but can become exploitable once the application is running. This includes vulnerabilities like cross-site scripting (XSS), SQL injection, and insecure server configurations.

While DAST offers a valuable perspective on potential runtime vulnerabilities, it also comes with its set of challenges. DAST can sometimes miss vulnerabilities that are not exploitable in the running state, and it can produce false negatives, for example in the case of business logic vulnerabilities. However, many of these shortcomings are overcome by next-generation DAST solutions.

In this article:

SAST vs. DAST Tools: 5 Key Differences 

1. Stage of Implementation

SAST is implemented at the early stages of the software development lifecycle (SDLC). It analyzes source code or binary code for security vulnerabilities, even before the code is compiled and the application is running. This early detection allows for immediate remediation of potential vulnerabilities, saving time and resources.

On the other hand, DAST, also known as “black box testing,” is implemented after the application is running. It tests the application in its operating environment, simulating real-world attacks to identify vulnerabilities. 

While this approach may seem reactive, it provides a realistic view of the application’s security posture, essential for understanding its behavior under attack. In addition, modern DAST tools can be integrated into the software development lifecycle (SDLC), so they can be run during testing stages, long before the application is in production.

2. Nature of Testing

SAST analyzes the source code or binary code. It examines the application from the inside, looking for common coding errors and security loopholes. It’s a proactive approach that aims to prevent security threats from the ground up.

In contrast, DAST examines the application from the outside. It interacts with the application’s exposed interfaces, treating the application as a black box without any knowledge of its internal workings. This approach detects vulnerabilities that may not be apparent during the development process but could be exploited when the application is in its operating environment.

3. Depth vs. Breadth

SAST provides depth—it can identify vulnerabilities deep within the code, which may not become apparent until specific conditions are met. It provides detailed insights into the code, making it a great tool for developers who want to understand and improve their code’s security.

DAST, meanwhile, offers breadth—it tests the application’s entire exposed surface, identifying vulnerabilities that may arise from the interaction between different parts of the application. DAST tools can be used to test thousands of possible attack patterns. While it may not provide the same level of detail as SAST, it provides a comprehensive view of the application’s security, making it invaluable for assessing the application’s overall risk. 

4. Vulnerabilities Detected

SAST is excellent at detecting issues like buffer overflows, SQL injections, and cross-site scripting (XSS) at the code level. It can also identify insecure coding practices that could potentially lead to security vulnerabilities.

While DAST can also detect these types of vulnerabilities by simulating attacks, it excels in identifying runtime vulnerabilities such as server configuration errors, application-level denial of service (DoS) attacks, and other vulnerabilities that result from the application’s interaction with its environment. It’s invaluable for detecting vulnerabilities that aren’t code-related, which SAST may miss.

5. Potential for False Positives and Negatives

No tool is perfect, and both SAST and DAST have their potential for false positives and negatives. False positives—where the tool incorrectly identifies a vulnerability—are common in SAST due to its in-depth code analysis. It can sometimes misinterpret safe code as vulnerable, leading to unnecessary remediation efforts.

DAST, on the other hand, has a higher likelihood of false negatives—where it fails to detect a real vulnerability. Its black-box approach can miss vulnerabilities hidden deep within the application’s code or those that only become apparent under specific conditions. 

However, DAST’s false positives are generally lower than SAST as it tests the application in its running state, providing a more realistic view of potential vulnerabilities. In addition, next-generation DAST solutions use fuzzing and AI technology to reduce false positives and negatives to virtually zero.

Related content: Read our guide to DAST tools

Combining SAST and DAST for Comprehensive Security 

While SAST and DAST have their differences, they are not mutually exclusive. In fact, using them in conjunction provides a more comprehensive view of the application’s security, addressing the limitations of each tool.

Incorporating both SAST and DAST into the SDLC can significantly enhance the security coverage. SAST can be used in the early development stages to identify and rectify potential vulnerabilities at the code level. DAST can then be implemented once the application is running, to detect any runtime vulnerabilities and assess the application’s behavior under attack conditions.

This combination provides a holistic view of the application’s security, ensuring that both code-level and runtime vulnerabilities are identified and mitigated. It allows for a proactive and reactive approach to security, ensuring that all bases are covered.

Related content: Read our guide to dast vs penetration testing.

Bright Security: The Ultimate Next-Generation DAST Solution

Bright Security tests every aspect of your apps. It enables you to scan any target, including web applications, internal applications, APIs (REST/SOAP/GraphQL), websockets, and server side mobile applications. It seamlessly integrates with the tools and workflows you already use, automatically triggering scans on every commit, pull request or build with unit testing. Scans are blazing fast, enabling Bright to work in a high velocity development environment.

Instead of just crawling applications and guessing, Bright interacts intelligently with applications and APIs. Our AI-powered engine understands application architecture and generates sophisticated and targeted attacks. By first verifying and exploiting the findings, we make sure we don’t report any false positives. 

Key features include:

  • Seamlessly integrates with existing tools and workflows—works with your existing CI/CD pipelines. Trigger scans on every commit, pull request or build with unit testing.
  • Spin-up, configure and control scans with code—one file, one command, one scan with no need for UI-based configuration.
  • Super-fast scans—interacts with applications and APIs, instead of just crawling them and guessing. Scans are made faster by an AI-powered engine that can understand application architecture and generate sophisticated and targeted attacks.
  • No false positives—uses AI analysis and fuzz testing to avoid returning false positives, so developers and testers can focus on releasing code.

Get a free plan and try Bright Security today!

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