IAST vs. DAST: 5 Key Differences, Pros/Cons & How to Choose

What Is DAST? 

Dynamic application security testing (DAST) is a method for evaluating the security of web applications. It works by simulating external attacks to identify vulnerabilities in a running application. DAST is deployed against live applications, often not requiring access to source code. 

By interacting with the application similarly to potential threats, it discovers security flaws that could be exploited by attackers. DAST tools automate the scanning process, providing detailed reports of discovered vulnerabilities. 

This methodology mimics real-world attack vectors and identifies security weaknesses that could be missed during code reviews. However, it is limited to testing only exposed interfaces and cannot access or analyze source code for deeper issues.

How DAST Works 

DAST operates by interacting with a running web application from the outside, simulating the behavior of an external attacker. The process typically begins with the DAST tool crawling the application to map its structure, including URLs, forms, and input fields. 

Once the application’s architecture is mapped, the tool launches a series of automated attacks, such as SQL injection, cross-site scripting (XSS), and other common exploits, targeting the identified components.

DAST tools analyze the application's responses to these simulated attacks, looking for unexpected behavior, error messages, or any sign that the application is handling input insecurely. For example, if an input field doesn’t properly sanitize user input, the DAST tool might detect this as a vulnerability that could be exploited in a real-world attack.

DAST does not require access to the underlying source code. It operates as a black box, focusing on how the application behaves during runtime. After the tests are completed, the tool generates a report detailing the discovered vulnerabilities, often with recommendations for remediation.

Related content: API Security: Threats, Tools, and Best Practices

What Is IAST? 

Interactive application security testing (IAST) is an approach to identifying security vulnerabilities within applications. Unlike other testing methods, IAST integrates with the application, combining elements of both static and dynamic analysis. 

It dynamically analyzes the code and provides real-time feedback while the application is running, offering insight into the security posture during development and testing phases. IAST tools are embedded within the application or its runtime environment, allowing continuous monitoring of code execution. 

This live interaction provides a more detailed view of vulnerabilities compared to surface-level scanning. With real-time data capture, developers receive immediate insights into potential issues, making it easier to find and fix security flaws throughout the development lifecycle.

How IAST Works 

IAST functions by embedding sensors within the application or its runtime environment to monitor its behavior during execution. These sensors are integrated into the application’s code or runtime framework, enabling the IAST tool to observe the application in action, including how data flows through it, how functions are executed, and how different modules interact.

Unlike DAST, which tests from the outside, IAST combines dynamic analysis with elements of static analysis. As the application runs, the IAST tool monitors various aspects of the execution, such as method calls, data flows, and configuration settings. 

This real-time monitoring allows IAST to detect vulnerabilities that are difficult or impossible to identify with external testing alone, such as insecure data handling practices, logic errors, and security misconfigurations.

IAST tools typically provide immediate feedback to developers, which is particularly beneficial during the development and testing phases. The insights provided by IAST tools help developers understand the root cause of vulnerabilities, making it easier to fix issues.
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DAST vs IAST: The Key Differences 

Here are some of the main differences between these two approaches to application security testing.

1. Approach

DAST uses a black-box approach, focusing on testing the application's exposed functionalities without internal access. This is similar to a simulated external attack, assessing vulnerabilities as if by a hacker. It aids in uncovering vulnerabilities related to user interactions and input handling.

IAST combines elements of black-box and white-box testing by embedding within the application. It observes code execution in real time, offering a deeper and context-aware analysis of potential vulnerabilities. It provides insights at the code level, including data flow and logic errors that may not be visible from the surface.

2. Testing Method

DAST's testing method relies on attack simulation from outside the application. It uses automated tools to scan the application for security threats, analyzing its responses to identify weaknesses. This requires minimal knowledge of the system internals and discovers issues observable at the user interface or API level.

IAST's method involves integrating directly into the application environment. Its sensors collect real-time data about application behavior during execution, identifying security flaws by monitoring various code paths. This method is useful for detecting vulnerabilities such as misconfigurations and unsafe coding practices embedded in the system.

3. Performance

DAST may impact application load as it simulates attack vectors, potentially affecting the user experience during scan periods. These tests are usually run in separate environments to mitigate this effect, ensuring the live application remains unaffected. However, the need for extensive setup and interpretation of results can lead to slower security assessments.

IAST, being fully integrated, offers performance insights without significantly impacting the application's operation. By working within the development environment, IAST operates alongside normal processes, minimizing disruptions. 

4. Information Gathering

DAST collects information by engaging with the application from an external standpoint. It analyzes how the application reacts to different simulated attacks, focusing on input fields, URLs, and exposed APIs. The aim is to gather data on how real-world attacks could exploit visible vulnerabilities. However, it may miss internal issues not exposed externally.

IAST captures detailed data on the application's execution flow. This approach aids in gathering information on code behavior, data exchanges, and API communications that external testing might overlook. 

5. Ease of Use

DAST is generally easier to set up and initiate since it requires no code modifications. It quickly integrates into existing workflows, making it accessible for teams with limited resources. However, interpreting the results can be complex, requiring skilled personnel to analyze the output accurately and address detected vulnerabilities.

‍IAST requires more initial setup, involving embedding agents into the application or development pipeline. However, IAST results are often easier to understand as they offer contextual information integrated with the application's code.

Tzvika Shneider

CEO, Pynt

Tzvika Shneider is a 20-year software Security industry leader with a robust background in product and software management.

Tips from the expert

• Combine DAST with Web Application Firewalls (WAFs): DAST can help identify attack vectors that a WAF should block. Use DAST findings to tune your WAF rules, which can provide an additional layer of security by blocking detected vulnerabilities before they are exploited.
• Use IAST in development sprints for real-time feedback: Incorporate IAST tools early in the development lifecycle to provide developers with immediate feedback on security flaws. This proactive approach helps catch vulnerabilities as the code is being written, making it easier to fix issues before they become deeply embedded.
• Automate DAST and IAST in your CI/CD pipeline: For continuous security, integrate both DAST and IAST tools into your CI/CD pipeline. Automated scans can run with every build, ensuring that new code is tested for security vulnerabilities before it reaches production.
• Focus on API security with DAST and IAST:Both DAST and IAST can be crucial for API security testing. Ensure that your security testing strategy includes endpoints and interactions specific to APIs, as these are common attack vectors. IAST, in particular, can provide insights into how internal API calls are handled.
• Develop detailed incident response procedures based on DAST and IAST outputs: Use the insights from both DAST and IAST to create detailed incident response procedures. Knowing which vulnerabilities are most likely to be exploited can help prepare specific responses, reducing the impact of potential breaches.

DAST Pros and Cons

Advantages:

1. Realistic testing: DAST simulates real-world attacks on a running application, making it effective at identifying vulnerabilities that could be exploited by actual attackers.
2. No access to source code required: Since DAST functions as a black-box testing method, it doesn't require access to the application's source code. This makes it suitable for assessing third-party applications or situations where source code is unavailable.
3. Ease of integration: DAST tools are relatively easy to integrate into existing security workflows. They can be deployed quickly and require minimal configuration, allowing teams to start testing without significant setup or changes to the development process.
4. Broad coverage: By testing the application's exposed interfaces, DAST can identify a range of vulnerabilities, including those related to input validation, authentication, and session management.

Disadvantages:

1. Limited to exposed interfaces: DAST can only test what is visible from the outside, meaning it might miss vulnerabilities that exist within the internal code structure or configurations that are not exposed through the application’s interfaces.
2. Potential for false positives: Since DAST tests applications without understanding the internal logic, it may report false positives—flagging issues that aren't actually vulnerabilities.
3. Performance impact: Running DAST against a live application can impact its performance, particularly if the test involves simulating high-volume attack scenarios. This may affect users or require testing to be conducted in a non-production environment.
4. Limited insight into root causes: DAST identifies the symptoms of vulnerabilities (such as unexpected responses to malicious input) but often lacks the ability to diagnose the underlying code issues causing them.

IAST Pros and Cons

Advantages:

1. Comprehensive coverage: IAST provides a more in-depth analysis by monitoring the application’s internal workings in real time. This allows it to detect a wider range of vulnerabilities, including those related to data flow, configuration issues, and business logic errors.
2. Immediate feedback: IAST tools offer real-time feedback to developers, which is useful during the development and testing phases. This continuous monitoring enables developers to fix security issues as they arise.
3. Low false positives: By understanding the application's internal logic and execution flow, IAST significantly reduces the likelihood of false positives compared to DAST. The contextual insights provided help ensure that flagged issues are genuine vulnerabilities.
4. Ease of remediation: IAST tools often provide detailed information about the exact location and nature of vulnerabilities within the code. This makes it easier for developers to pinpoint and address issues.

Disadvantages:

1. Complex setup: Implementing IAST requires embedding sensors or agents within the application or its runtime environment, which can be more complex and time-consuming than setting up DAST.
2. Performance overhead: Although intended to minimize disruption, IAST can introduce some performance overhead, particularly in large or complex applications. Continuous monitoring during execution might slow down development or testing environments.
3. Dependence on application environment: IAST's effectiveness can be influenced by the environment in which the application runs. Variations in deployment configurations or runtime environments may impact the accuracy of the testing results.

Requires source code or runtime access: Unlike DAST, IAST needs access to the application’s source code or runtime environment, which may not always be feasible, especially for testing third-party applications or when security policies restrict such access.

IAST vs DAST: How to Choose 

Choosing between interactive and dynamic application security testing depends on several factors, including the stage of application development, available resources, and security goals:

• Application maturity: DAST is often more suitable for applications that are already in production or near completion, as it focuses on testing the external-facing aspects. IAST, on the other hand, is suitable for use throughout the development process, providing continuous feedback that helps developers address issues before deployment.
• Access to source code: If access to the source code is not feasible—due to third-party restrictions or security policies—DAST is the preferred choice since it operates without needing internal access. IAST requires access to the source code or runtime environment, which may not always be possible.
• Testing depth: For a more surface-level security check that focuses on exposed interfaces, DAST is effective. However, if deeper insights into the application's internal workings, including business logic and data flows, are necessary, IAST offers a more comprehensive solution.
• Development workflow: Organizations with a mature DevSecOps pipeline might prefer IAST for its integration with continuous integration/continuous deployment (CI/CD) processes. DAST, while easier to implement, may require additional steps to fit into automated workflows.
• Resource availability: DAST is generally easier to set up and requires fewer resources, making it suitable for teams with limited security expertise or smaller budgets. IAST, with its more complex setup and need for integration into the development environment, may require more dedicated resources and skilled personnel.
• Accuracy and false positives: If minimizing false positives is a priority, IAST offers better accuracy by providing contextual information that helps distinguish genuine vulnerabilities from false alarms. DAST, due to its external testing nature, might produce more false positives.

Complementing DAST and IAST with API Security Testing

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