Buchi Reddy B
CEO and Founder at Levo
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Even in 2016, as an Engineering Director, I consistently advocated for the value added by DAST scanners, even though my team was already equipped with SAST and SCA tooling.
DAST adoption has since surged, and for a good reason—it simulates real-world attacks during runtime, catching vulnerabilities in web applications as they progress through CI/CD pipelines into production.
However, despite its effectiveness in web application security, relying on DAST for API security ignores a dangerous blind spot for your DevSecOps teams.
DAST’s black-box approach, designed for GUIs and user-driven inputs, lacks the context that is essential to effectively test API Vulnerabilities.
Let me explain why DAST falls short in securing your APIs—and why a specialized approach is essential.
We’re not subscribing to the idea that DAST is dead—far from it.
DAST scanners are crucial in identifying vulnerabilities that SAST tools miss, especially XSS, SQL injection, and Cross-Site Request Forgery.
The core issue is that DAST was designed with web applications in mind, not APIs. The fundamental difference lies in their intended use and structure.
Web applications are built for user interaction through GUIs—buttons, forms, and other elements that make mapping and testing easier for a DAST tool. In contrast, APIs facilitate machine-to-machine communication, handling data and executing functions programmatically, often without a visible UI.
APIs don’t offer the visible surface area that web apps do. DAST tools rely on crawling and spidering, but you can’t crawl an API.
In modern environments, APIs are often embedded deep within application code, becoming visible only when specific backend processes trigger them.
Simply put, testing APIs with DAST is like searching for hidden rooms in a building without a map.
You might eventually stumble upon vulnerabilities but go through the sections below to understand why they are inefficient, incomplete, and risky.
One of the core limitations of DAST scanners in API security testing is their inherent nature as black-box testing tools.
By design, DAST operates without internal application knowledge—it tests without context. This works relatively well for web applications, where UI elements such as buttons, forms, and input fields show the scanner what to test. DAST scanners can follow a logical path through these elements, interacting with them as a user would, exposing potential vulnerabilities.
While DAST can follow predictable paths through web applications, it struggles with APIs, whose endpoints are typically hidden beneath logic and dynamic behavior layers.
An API’s functionality is hidden beneath the surface, remaining invisible at runtime unless called with specific HTTP methods and the correct request formats.
Without the context provided by a GUI, DAST tools struggle to locate, let alone test, API endpoints.
The problem is further compounded by how APIs are often buried within application code. In modern web applications, dynamic JavaScript code (through technologies like AJAX) is responsible for many backend API calls. These API interactions occur behind the scenes as part of the web app’s runtime behavior, often triggered only after a specific page or application state is loaded. Until JavaScript code is executed, the APIs it calls remain hidden—essentially "buried" within the application's backend logic.
For a DAST tool to detect these API calls, it must first load the relevant page, execute the JavaScript, and then attempt to capture the API request in real time.
This indirect method leaves plenty of room for missed APIs, incomplete testing, and unidentified vulnerabilities.
Without a proper API inventory—a catalog that includes internal, third-party, and partner APIs—DAST tools cannot determine which APIs exist or where to begin testing.
Even though maintaining an up-to-date API inventory is recommended by industry standards like the OWASP API Security Top 10 and mandated by compliance frameworks such as PCI DSS, more than 75% of surveyed enterprises admit they do not have a comprehensive inventory of their APIs.
Even if you could expose all your API endpoints, another significant problem arises: incomplete or inaccurate API documentation.
Unlike web applications, where DAST can infer behavior through visible inputs, APIs operate with a range of hidden parameters and payloads.
For example, an API may require 10-15 parameters in JSON or XML formats, each interacting with specific business logic. Lacking accurate documentation outlining each endpoint’s behavior and the correct request formats, DAST tools are effectively guessing.
Even if DAST tools are equipped with modified Swagger files, their effectiveness relies entirely on the accuracy of the provided documentation.
Documentation that is rarely accurate or comprehensive. A recent survey found that over 65% of enterprises admit their API documentation is incomplete.
It’s not just knowing where the endpoints are; it’s about understanding exactly how each one operates.
A single missing specification/parameter could be the difference between catching a vulnerability and leaving a backdoor wide open for attackers.
While API Inventory and Documentation lay the groundwork for API security testing, they are not enough on their own.
Effective API security testing requires more—specifically, context-specific payload generation and authentication automation—additional areas where traditional DAST tools fall short.
Modern applications use a variety of authentication schemes—OAuth, JWT, API keys, and more—requiring intricate credential management.
DAST tools often fail here, requiring manual management of sessions, tokens, and protocols. This adds inefficiencies and leaves room for human error, leading to incomplete testing.
Equally crucial is understanding user context. Real-world interactions with applications are often unpredictable and complex. Without context, DAST tests may miss vulnerabilities that could be exploited under genuine conditions, such as unauthorized data access.
Take the example of BOLA with a "get account balance" API.
A DAST tool might test this API using the account holder’s credentials and account ID. If everything is functioning correctly, the test will pass.
However, detecting a BOLA vulnerability requires accessing the account balance with someone else’s credentials.
The challenge is that DAST tools typically do not dynamically substitute parameters. They use the same user credentials throughout the test, missing out on potential unauthorized access scenarios.
Unlike a DAST tool, an attacker using tools like Postman or cURL can directly interact with the API, bypassing the web interface and exploiting many such vulnerabilities effectively.
DAST’s shortcomings in API security boil down to one thing: lack of context. Unlike web apps with visible, user-driven elements, APIs operate in the background, exchanging data with other applications. Here’s how we’ve built Levo to automatically and holistically test your APIs:
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