SAST, DAST, IAST, and RASP: Key Differences and How to Choose

Our 2024 State of Software Quality report shows that more software teams are using automated application security testing to address increasing cyber threats. However, implementing the right security testing method can be challenging.

Static Application Security Testing (SAST), Dynamic Application Security Testing (DAST), Interactive Application Security Testing (IAST), and Runtime Application Self-Protection (RASP) are among the most prevalent automated testing techniques today. While combining these methods is essential for thorough application coverage and robust security, understanding the strengths of each technique is crucial for creating a comprehensive security testing strategy for your organization.

This article aims to demystify SAST, DAST, IAST, and RASP, providing a clear understanding of how these application security testing methods operate. We'll not only explain how each technique works but also compare their strengths and weaknesses and provide guidance on when to use each method to protect your software from vulnerabilities. By the end of this article, you'll have a clear understanding of how to effectively implement these techniques to ensure the security and integrity of your applications.

What is Application Security Testing?

Application Security Testing (AST) involves examining software applications to identify, report, and fix code and application infrastructure vulnerabilities. It is an indispensable practice for organizations seeking to strengthen their applications and protect their data against the ever-changing landscape of threats. 

Here are a few reasons why application security testing is important:

• Prevents attacks by identifying and fixing software vulnerabilities.
  
  
• Ensures applications comply with industry regulations, such as the General Data Protection Regulation (GDPR), the Health Insurance Portability and Accountability Act (HIPAA), and the Payment Card Industry Data Security Standard (PCI-DSS).
  
  
• Reduces the cost of fixing software security issues, as fixing vulnerabilities during the development phase is much cheaper and easier than after a breach.
  
  
• Improves software quality.

SAST vs. DAST vs. IAST vs. RASP: Comparison

Every testing method has a unique purpose, depending on the testing approach and stage in which it is utilized. Understanding the differences can help you implement a layered security testing approach that fits your needs. We will discuss each method in further detail, but let’s first explain the main distinctions among them.

SAST (Static Application Security Testing)

SAST, or Static Application Security Testing, is a white-box security testing methodology that analyzes your application's source code, byte code, or binary code to identify potential security vulnerabilities and issues, such as SQL injection, cross-site scripting (XSS), and buffer overflows.

SAST acts like a code detective, thoroughly examining your application’s source code, line by line, before deployment. 

For instance, consider a scenario where a developer writes a function to handle user inputs for login credentials. A SAST tool can scan this code and identify potential SQL injection points by flagging lines (the concatenation of username and password variables) where user inputs are directly concatenated into SQL queries without proper sanitization.

public boolean validateUser(String username, String password) {
    String query = "SELECT * FROM users WHERE username = '" + username + "' AND password = '" + password + "'";
    // Execute query...
}

A SAST tool would then suggest the use of prepared statements to prevent SQL injection:

public boolean validateUser(String username, String password) {
    String query = "SELECT * FROM users WHERE username = ? AND password = ?";
    PreparedStatement pstmt = connection.prepareStatement(query);
    pstmt.setString(1, username);
    pstmt.setString(2, password);
    // Execute prepared statement...
}

SAST is a powerful and proactive tool that can help identify and eliminate potential security issues and vulnerabilities early in development. However, one significant drawback of SAST is its inability to uncover vulnerabilities during runtime, like configuration errors or runtime dependency issues. SAST is most effective when used as part of a layered approach with other application security testing methods.

DAST (Dynamic Application Security Testing)

Dynamic Application Security Testing (DAST) assesses applications by simulating attacks in a live production environment. DAST uses a black-box approach to examine an application from an external perspective.

Unlike SAST, DAST is a reactive approach that helps uncover vulnerabilities post-deployment by sending various malicious inputs to the application and reviewing responses to find security vulnerabilities, such as insecure server configurations, authentication flaws, injection attacks, session hijacking, and cross-site scripting (XSS).

For example, DAST can identify problems with how users log in and manage their sessions, like when passwords are easy to guess, sessions are kept open for too long, or sessions aren’t handled securely. DAST can identify vulnerabilities that are unlikely to arise during testing but pose a risk in real-life use.

IAST (Interactive Application Security Testing)

Interactive Application Security Testing (IAST) combines elements of Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST) to enhance application security testing. 

IAST works by deploying sensors and agents within running applications. These sensors and agents monitor application behavior during testing by analyzing data flow and execution. This internal access provides IAST with a broader range of data, resulting in more extensive coverage than source code analysis (SAST) or website scanning (DAST). It’s like having a security camera inside your app, capturing everything that happens and pointing out potential weak points.

IAST embeds agents within the application to monitor data flow across all layers, from the front end to the backend. This broader range of data provides a more detailed understanding of how user inputs are processed and how vulnerabilities are exploited. For instance, if a user attempts to input malicious SQL code, IAST can trace the data flow from the frontend to the backend API, identifying the exact locations and contexts of potential SQL injection vulnerabilities. This level of insight enables developers to prioritize and remediate vulnerabilities more effectively.

RASP (Runtime Application Self-Protection)

Runtime Application Self-Protection (RASP) is a security technology built into an application to detect and prevent attacks in real-time. Unlike SAST, DAST, and IAST, which are primarily testing tools, RASP operates as a continuous security measure. It is embedded within a running application, consistently monitoring activity for indications of suspicious behavior that might signal an attack. In response to real-time attacks, RASP terminates an attacker’s session and alerts defenders to the attack.

For example, RASP can help protect your application by stopping hackers from running their own code on your server (RCE or Remote Code Execution).

One challenge with RASP is that it can lead development teams to feel overly confident about security. They might start thinking, "If we make a mistake, RASP will catch it," and become less diligent about following security best practices. 

Demystifying SAST, DAST, IAST, and RASP Use Cases

Deciding which application security testing method to use is crucial for keeping your software secure. We recommend a layered approach that combines different methods to maximize protection. By understanding the strengths of each tool, you can effectively decide when to use SAST, DAST, IAST, and RASP, ensuring comprehensive security coverage for your applications.

SAST: Early Security Champion

• Integrate SAST tools into your CI pipeline to automatically scan code for vulnerabilities as you develop. This allows you to catch and fix issues early, saving time and resources compared to fixing them later.
  
  
• SAST excels at identifying common coding errors that can lead to security vulnerabilities, like Cross-Site Scripting (XSS) and SQL injection.

DAST: Simulating the Attacker

• Use DAST during the testing phase to simulate real-world attacks and identify vulnerabilities that an external attacker might exploit.
  
  
• DAST is particularly helpful for finding issues related to runtime behavior, like insecure user input handling, authentication weaknesses, and configuration errors.
  
  
• DAST is a good choice when you lack access to the source code or need to test your application's behavior under simulated attacks.

IAST: Real-Time Security Insights

• IAST combines static code analysis with dynamic testing, providing real-time vulnerability feedback during the testing phase.
  
  
• This approach offers a more comprehensive view of your application's security posture by identifying potential code vulnerabilities and verifying their exploitability during testing.
  
  
• IAST is ideal for complex applications where both static and dynamic testing are crucial.

RASP: Continuous Protection in Production

• Deploy RASP in your production environment for continuous security monitoring. It detects and mitigates threats as they arise, offering real-time application protection.
  
  
• RASP is valuable for applications that require ongoing security without frequent updates.

Secure Your Applications With a Layered Approach

A layered approach incorporating SAST, DAST, IAST, and RASP tools is essential to ensure robust application security. By combining the strengths of each method, you can:

• Identify vulnerabilities early with SAST
  
  
• Detect runtime issues with DAST
  
  
• Monitor the application's internal behavior with IAST
  
  
• Protect applications in production with RASP

For a seamless and integrated application security testing experience, consider Codacy. Codacy offers SAST across over 40 programming languages, software composition analysis, and automated security code reviews. And, with our newly added DAST capabilities, Codacy Security is poised to provide a comprehensive solution that covers your applications from development to deployment. Sign up for a free trial today.