Two of the most popular methodologies used to identify and rectify vulnerabilities in applications are Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST). Both aim to secure software, but their methods differ. It's not about selecting SAST vs DAST; for optimal security, it's best to integrate both. This article dives into the distinctions between the two and discusses how to combine them for comprehensive application security.

1. What is SAST?

Static Application Security Testing (SAST), often referred to as "white-box testing", is a testing methodology that identifies vulnerabilities by examining the source code, bytecode, or binary code of an application without executing it.

Key Features of SAST

Early Detection: Since SAST evaluates code at the development phase, it can identify vulnerabilities early in the software development lifecycle (SDLC).
Comprehensive Analysis: SAST tools can review the entire codebase, ensuring a thorough examination.
Language-Specific: Many SAST tools are tailored for specific programming languages, offering precise vulnerability detection.

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2. What is DAST?

Dynamic Application Security Testing (DAST), often termed "black-box testing", is a testing methodology that assesses running applications, typically from an external perspective. DAST focuses on identifying vulnerabilities that become evident only during runtime. DAST evaluates the security of APIs in real-world scenarios, identifying vulnerabilities that could be exploited during runtime

Key Features of DAST

Runtime Analysis: DAST evaluates applications during their execution, identifying vulnerabilities manifesting at runtime. DAST provides comprehensive API Security Testing by assessing vulnerabilities in real-world scenarios
Environment Specific: DAST can identify issues related to the application's environment, such as server configurations.
No Access to Source Code: DAST doesn't require access to the application's source code, making it suitable for third-party applications.

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3. SAST vs DAST: The Differences

Criteria	SAST	DAST
Nature of Testing	"White-box testing" that examines the application's internals, such as source code, bytecode, or binary code without running the application.	"Black-box testing" that evaluates the application from an outsider's perspective while it's running, often in real-world scenarios.
Point of Evaluation	Evaluates the code during the development phase, even before the application is operational.	Assesses the application once it's operational, typically in a staging or production environment.
Depth of Analysis	Provides a deep, comprehensive analysis of the codebase.	Offers a surface-level analysis, focusing on runtime vulnerabilities.
Access to Source Code	Requires access to the application's source code, bytecode, or binary code.	Doesn't need access to the source code, ideal for third-party applications.
Feedback and Remediation	Provides detailed feedback, pointing directly to problematic code lines for easier remediation.	Identifies vulnerabilities but might not provide detailed feedback on fixes due to lack of code insight.
Speed and Efficiency	Can be time-consuming for large codebases but efficient in catching vulnerabilities early.	Generally faster, focusing on runtime behavior but might miss non-manifesting vulnerabilities.
Types of Vulnerabilities Detected	Identifies vulnerabilities like input validation errors, insecure coding practices, and potential data leaks.	Detects issues like session management flaws, authentication problems, and server configuration vulnerabilities.

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4. Combining SAST and DAST

Both SAST and DAST are powerful on their own, their combined use ensures that applications are examined from both a code and operational perspective. It's not about SAST vs DAST; using both ensures detecting a wider range of vulnerabilities and fosters a culture of continuous security improvement throughout the application's lifecycle. Here's a deeper dive into the benefits and strategies of combining these two methodologies:

Holistic Security Coverage

SAST: By analyzing the codebase, SAST identifies vulnerabilities at the very root, often before they manifest during runtime. This early detection ensures that the foundational code of the application is secure.
DAST: By testing the running application, DAST identifies vulnerabilities that only become evident during execution, especially the business logic vulnerabilities that arise from user interactions, server configurations, or third-party components.

Efficient Remediation

SAST: With its detailed feedback, developers can pinpoint the exact location of vulnerabilities in the code, leading to quicker and more accurate remediation.
DAST: While DAST might not provide the exact code location of a vulnerability, it offers a real-world perspective, helping developers understand how vulnerabilities can be exploited, which can guide the remediation process.

Continuous Security Integration

SAST: Integrating SAST tools into the early stages of the software development lifecycle (SDLC) ensures that code is continuously checked for vulnerabilities as it's written.
DAST: Incorporating DAST into post-deployment stages or continuous monitoring setups ensures that the application is regularly checked for new vulnerabilities, especially those that might arise due to changes in the environment or newly discovered exploits.

Cost Efficiency

SAST: By catching vulnerabilities early in the SDLC, SAST can save significant costs, as addressing issues during the development phase is often cheaper than post-deployment fixes.
DAST: While DAST might identify vulnerabilities later in the SDLC, it can prevent potential exploitation in real-world scenarios, potentially saving organizations from financial damages.

Comprehensive Feedback Loop

SAST: Feedback from SAST can be used to educate developers about secure coding practices, leading to better code quality over time.
DAST: Feedback from DAST can inform developers and operations teams about potential runtime vulnerabilities, leading to better deployment practices and environment configurations.

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In Conclusion

It's not a matter of choosing SAST vs DAST, as both have distinct benefits. Static Application Security Testing and Dynamic Application Security Testing have distinct approaches and advantages, and combining the two offers a comprehensive security assessment, ensuring that applications are robust and free from vulnerabilities.

Use SAST when you want to catch vulnerabilities early, have access to the source code, and need a deep dive into the codebase.
Use DAST for runtime analysis, for third-party applications, and when you need an external perspective on the application's security.

For the most thorough security protection, it's recommended to incorporate both SAST and DAST into your software development and deployment processes.

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