SAST vs. DAST: Application Security Testing Tools

September 21, 2023
By Aaron Linskens

8 minute read time

As the threat landscape continues to evolve, organizations face a formidable challenge: Ensure the security of their software applications.

Even when software engineers meticulously adhere to secure coding guidelines, vulnerabilities and malware can still emerge in production code. This stark reality underscores the indispensable function of application security testing as a robust practice of defense against security vulnerabilities lurking within software.

The realm of application security testing contains the following methodologies:

• Static Application Security Testing (SAST)
• Dynamic Application Security Testing (DAST)
• Interactive Application Security Testing (IAST)
• Runtime Application Self Protection (RASP)

While all these approaches help enhance application security by addressing different aspects and stages of the software development life cycle (SDLC), the scope of this blog post only encompasses SAST and DAST.

In this post, we explore the core concepts, advantages, and limitations of SAST and DAST, emphasizing their pivotal roles in application security. We also discuss how these application security testing methods can be integrated into DevSecOps pipelines for continuous security assessments and stronger defenses against the rising tide of threat actors.

Static Application Security Testing (SAST)

What Is SAST?

SAST, or static application security testing, focuses primarily on analyzing the source code and underlying software components of an application. It is a white-box testing methodology, which offers testers complete knowledge of the application being assessed, including access to source code and design documents.

This examination takes place during the early stages of the SDLC, typically before the code is compiled or deployed. SAST tools execute a comprehensive scan of the source code, configuration files, and other development artifacts to uncover potential security vulnerabilities and coding errors.

Why Is SAST Important?

SAST delivers an in-depth view of the application's structure and logic.

By examining the codebase from within, static application security testing tools can identify vulnerabilities, such as:

• SQL injection
• Cross-site scripting (XSS)
• Insecure authentication mechanisms

This inside-out approach empowers software engineers and security teams to pinpoint issues at their root and address them proactively, preventing their manifestation in the runtime environment.

Another critical function of SAST is its ability to identify vulnerabilities early in the development process. By catching security flaws during coding and design phases, SAST helps ensure that software is built with security in mind from the outset.

Dynamic Application Security Testing (DAST)

What Is DAST?

Dynamic application security testing (DAST) examines running applications in their runtime environments, assessing the applications from an outsider's perspective and mimicking the approach of potential attackers. It is a black-box testing methodology, meaning it operates with limited or no insight into the application's internal architecture or source code.

DAST tools interact with the application much like a real user, sending requests and analyzing responses to uncover application exploits.

Unlike SAST, DAST does not require access to the application's source code. This makes it a valuable technique for testing third-party or legacy applications where source code may not be available.

DAST can uncover vulnerabilities that manifest during runtime, such as:

• Session management issues
• Misconfigurations
• Server-side vulnerabilities

Why Is DAST Important?

Dynamic application security testing plays a crucial role in identifying real-world threats and potential vulnerabilities that threat actors might exploit. By evaluating the application's security posture under real-world conditions, organizations gain a deeper understanding of their exposure to external attacks. DAST proves indispensable for simulating attacks and obtaining insights into security posture from an external vantage point.

Differences between SAST and DAST

Applicability in the SDLC

Static application security testing is applied during the pre-runtime phases of the SDLC, including design and coding, helping identify vulnerabilities before code execution.

Dynamic application security testing is best suited for assessing runtime vulnerabilities. It is typically utilized after the application is deployed and actively running — usually in a pre-production environment.

Types of Vulnerabilities Detected

SAST excels at identifying vulnerabilities related to code quality, such as code injection, insecure data storage, and authentication issues. It also helps uncover design flaws that can lead to security vulnerabilities.

DAST focuses on vulnerabilities that manifest during runtime, including issues related to the application's configuration, session management, and external interactions.

Advantages and Limitations

SAST advantages:

• Early vulnerability detection: SAST's ability to analyze source code during development enables the identification of vulnerabilities at an early stage, reducing the cost and effort required for remediation.
• In-depth analysis of source code: SAST tools perform a thorough examination of source code, offering extensive insight into the application's inner workings, including code quality, structure, and potential security issues.
• Integration into the development process: By seamlessly integrating with the development process, SAST allows security assessments as code is written and reviewed.
• Ability to catch design flaws: SAST can detect design flaws and architectural vulnerabilities, which are challenging to identify during runtime testing.

SAST limitations:

• Limited coverage for runtime vulnerabilities: SAST primarily focuses on static code analysis and may not effectively identify runtime vulnerabilities or configuration-related issues.
• False positives: SAST tools may occasionally produce false positives, highlighting code as vulnerable when it is not. Organizations need to invest time in triaging and verifying these findings, which can be resource-intensive.
• Need access to the source code: SAST requires access to the application's source code. This may not be feasible for third-party or legacy applications, limiting its applicability in certain scenarios.

DAST advantages:

• Real-world testing: DAST simulates real-world threats, providing insights into how an application behaves under authentic conditions and the vulnerabilities that might be exploited.
• Detection of runtime vulnerabilities: DAST excels at identifying vulnerabilities that manifest during runtime, such as session management issues, server misconfigurations, and other runtime-specific problems.
• No need for access to source code: DAST operates without access to the application's source code, making it suitable for third-party applications or situations where source code is unavailable.
• Uncover vulnerabilities caused by configuration issues: DAST is particularly adept at finding vulnerabilities arising from misconfigurations and security settings.

DAST limitations:

• Limited visibility into the application's internal logic: DAST evaluates an application from an external perspective, limiting its ability to access or understand the internal logic of the software. For example, it may not discern how data flows within an application or identify certain vulnerabilities within complex business logic.
• Inability to identify certain types of vulnerabilities: DAST may struggle to identify vulnerabilities that require knowledge of application behavior, data flow, or specific dependencies. For instance, it may not effectively detect business logic flaws or access control issues.
• Reliance on a running instance of the application: DAST relies on a live, running instance of the application, which means it may not identify issues in offline or development environments. Moreover, it may not be suitable for applications with extensive login processes or intricate workflows that DAST struggles to navigate effectively.

Integrating SAST and DAST in DevSecOps

In the case of security testing for web applications, embedding security within the DevOps pipeline is critical to ensure applications are developed and deployed securely.

Explore the application security testing concepts below to see how your organization could successfully implement this integration, along with key tools and technologies that can facilitate the process.

CI/CD Pipeline Integration

To ensure continuous security assessments, integrate both SAST and DAST into your continuous integration/continuous deployment (CI/CD) pipelines. Leverage CI/CD orchestration tools to seamlessly weave security scans into your development and deployment workflows.

Automation Is Key

Utilize automation to trigger SAST and DAST scans automatically with every code commit or deployment. This can be achieved through scripting and configuration within your CI/CD pipeline.

Leverage SAST Tools

For SAST integration, consider leveraging concepts such as static code analysis and code review. These processes analyze the source code for potential vulnerabilities and issues early, making them a critical component in secure coding practices.

Unified Reporting and Remediation

Strive for unified reporting that consolidates findings from both SAST and DAST scans. This helps streamline the remediation process by presenting a single view of vulnerabilities and their priorities.

Shift Left Security

Embrace a Shift Left mentality, where security is a core consideration from the beginning of the development process. Encourage developers to use application security testing concepts during coding and design phases, reducing the likelihood of security vulnerabilities entering the codebase in the first place.

Benefits of a Unified Approach

A unified approach to security testing for web applications that incorporates both SAST and DAST in a DevSecOps pipeline offers comprehensive security coverage. While SAST thrives at early vulnerability detection and in-depth source code analysis, DAST thrives in real-world testing scenarios.

A Unified Approach for Secure Software Development

Together, SAST and DAST offer a holistic view of an application's security, reducing the risk of undetected vulnerabilities infiltrating production environments. SAST identifies issues early in the development process, while DAST excels in real-world testing scenarios.

While each methodology has its unique strengths, their integration within a DevSecOps pipeline offers a comprehensive approach to fortifying application security. Unified security testing for web applications like SAST and DAST not only reduces the risk of security vulnerabilities, but also allows organizations to confidently deliver more secure software to their users.