Dynamic application security testing
In the relentless, high-speed world of modern software development, security is a constant challenge. Applications are more complex than ever, relying on a vast network of microservices, third-party libraries, and APIs. Dynamic application security testing (DAST) is an indispensable part of a robust application security (AppSec) strategy, providing a crucial, "outside-in" perspective on an application's defenses.
What is DAST?
DAST, often referred to as dynamic analysis, is a cybersecurity testing method that identifies security weaknesses and misconfigurations in running applications. Unlike testing methodologies that analyze an application's source code before it's executed, DAST scrutinizes the application from the outside, treating it as a black box (i.e., we cannot "look inside the machine").
This approach is invaluable because it mimics how an attacker or malicious user would interact with the application—without any prior knowledge of its inner workings, code, or underlying frameworks. A DAST tool sends a series of simulated attacks, or malicious payloads, to the application's endpoints and then analyzes its responses to identify potential vulnerabilities. The ultimate goal is to see if an attacker could exploit a particular weakness to gain unauthorized access, steal data, or disrupt the application's functionality.
At its core, DAST works through a methodical, multi-step process:
Mapping and crawling: A DAST tool first maps out the application's attack surface. It crawls the application to discover all its pages, links, APIs, and other entry points. This creates a comprehensive view of what a user—or an attacker—can interact with.
Simulating attacks: Once the map is created, the DAST tool begins to simulate a variety of common attacks. It sends malicious input to fields, headers, and other entry points, looking for anomalous responses. This includes attempts at SQL injection, cross-site scripting (XSS), cross-site request forgery (CSRF), and other well-known attacks.
Analyzing responses: The tool meticulously monitors the application's behavior in response to these attacks. If the application crashes, provides unexpected error messages, or grants unauthorized access, it indicates a potential vulnerability. For instance, a successful SQL injection attack provides proof that a vulnerability exists and is exploitable.
Generating reports: Finally, the DAST tool generates a detailed report outlining the identified vulnerabilities. The report typically includes the severity of each issue, potential attack scenarios, and, in some cases, evidence such as images or videos to support the findings.
Since DAST works on a running application, it is language-independent. The tool interacts with the application externally through its interfaces, so it doesn't matter if the application is written in Python, Java, or any other language. This flexibility makes DAST a valuable tool for testing a wide range of applications, including those with proprietary code or those built by third-party vendors where the source code is unavailable.
Why is DAST necessary?
DAST is a crucial component of any modern application security program for several key reasons that address the challenges of today's development landscape.
Identifying real-world, runtime vulnerabilities
DAST excels at finding vulnerabilities that only manifest when an application is active and interacting with its environment. This is an indispensable method that can effectively identify issues related to server configuration, authentication, and session management flaws, and how data is handled during transit. These are precisely the problems that an attacker would look for in a live system.
DAST offers a realistic perspective on the threats an application faces in an operating setting, helping organizations understand their exposure to cyberattacks. By simulating these threats, DAST provides irrefutable evidence—even proof of exploitation—that a vulnerability is not just a theoretical risk but a genuine, exploitable flaw.
Protecting against evolving threats
Modern applications are more complex than ever, and the attack surface is constantly expanding. Developers rely heavily on third-party and open-source components, often without a complete grasp of the entire codebase. This creates an ever-growing surface area for security vulnerabilities. Furthermore, bad actors are constantly devising new attack methods. DAST helps organizations stay ahead of these dynamic threats by testing how applications respond to new and emerging attack patterns.
Enforcing security practices and compliance
By integrating DAST into the development pipeline, teams can catch and address vulnerabilities before they make it into production and possibly lead to costly data breaches, significant financial loss, and irreparable damage to an organization's brand reputation. For many companies, DAST is also essential for adhering to industry standards and regulatory requirements. Many international standards, such as OWASP Top 10, PCI DSS, GDPR, and HIPAA, suggest or mandate regular security testing of applications that handle sensitive data. DAST helps organizations meet these requirements by providing an objective, outside-in assessment of their security posture.
DAST in the SDLC: shifting security left
DAST is typically performed at an advanced stage of the SDLC, once a working application is available in a staging, QA (quality assurance), or testing environment. However, modern DevSecOps practices emphasize "shifting left," which means embedding security checks as early as possible in the development process. DAST contributes to this approach by providing efficient and automated testing before an application is deployed into production, i.e., in pre-production environments.
By integrating DAST scans into continuous integration/continuous deployment (CI/CD) pipelines, security analysis can occur automatically with every code check-in or build, as long as there is a functional structure ready for interactive or dynamic evaluation. This allows developers to receive rapid feedback on potential security issues, enabling them to address these problems when they are still fresh in their minds. While a full scan may be time-consuming, targeted or incremental scans can be used during development cycles to provide quick feedback without disrupting workflow.
The benefits of this "shift left" approach with DAST are substantial:
Accelerated development: By catching vulnerabilities early on, developers can fix them quickly, preventing them from accumulating into complex, time-consuming problems later on. This minimizes rework and helps maintain development speed.
Reduced remediation costs: The later a vulnerability is discovered in the SDLC, the more expensive it becomes to fix. DAST's early intervention, even when performed in staging or QA environments, dramatically cuts down these costs.
Secure SDLC: Regular DAST scans contribute to a more secure SDLC by ensuring that multiple security considerations are embedded at every stage, from initial coding to final release.
DAST is typically the "last" opportunity to identify security issues before an application enters a production environment, where any undetected vulnerabilities can be exploited by threat actors. This makes it an essential part of the "final" safety net before an application, in each of its various versions, goes live.
What are the differences between DAST and SAST?
To better understand DAST, it is important to see how it fits into a comprehensive AppSec strategy and how it differs from other methodologies, particularly static application security testing (SAST) and software composition analysis (SCA). Let's look at an initial comparison:
Feature | DAST | SAST |
Testing method | Black-box testing (outside-in). | White-box testing (inside-out). |
Analysis | Analyzes a running application by simulating attacks. | Analyzes source code, bytecode, or binaries without executing the application. |
Visibility | No visibility into the internal operations or source code; treats the application as a black box. | Complete visibility into the application's source code and internal logic. |
When applied | Later in the SDLC, once there is a working application (e.g., in a test environment or production). | Early in the SDLC, as soon as code is written or committed. |
Vulnerability types | Runtime vulnerabilities, configuration issues, authentication flaws, server-side issues (e.g., XSS, broken authentication). | Code-level vulnerabilities, logic flaws, insecure coding practices (e.g., SQLi, buffer overflows, XXE). |
Programming language dependent? | No, it interacts with the application externally, regardless of its underlying language. | Yes, the tool needs to support the specific language(s) and frameworks used. |
False positives | Tends to produce fewer false positives as it tests real-world execution. | Tends to produce more false positives as it lacks runtime context. |
Remediation details | Reports that a vulnerability exists, but not the exact line of code. | Pinpoints the exact line of code, making remediation straightforward. |
Speed of scan | Can take longer, as it requires the application to be executable and involves simulating interactions. | Generally faster, as it doesn't require a running application. |
The differences between DAST and SAST highlight why they are complementary, not mutually exclusive. They largely detect different types of vulnerabilities and provide distinct insights. SAST excels at identifying code-level flaws early in the development cycle, while DAST fills a crucial gap by testing the live application much as an attacker would.
DAST, SAST and SCA
The third piece of the application security puzzle is SCA. While DAST focuses on the running application and SAST on the custom-written code, SCA focuses on the third-party components and open-source libraries that applications rely on. SCA tools scan these components to detect known vulnerabilities from public databases. To achieve a comprehensive security posture, it is recommended to use DAST, SAST, and SCA together. This way, organizations can gain a broad and unified view of their vulnerabilities, maximizing their ability to detect risks before applications are launched.
Advantages and disadvantages of DAST
Like any AppSec testing methodology, DAST has its strengths and weaknesses. Understanding these helps in its effective deployment.
Advantages of DAST
Identification of real-world vulnerabilities: DAST tests the application in its running state, mirroring "real-world" conditions. This approach helps uncover vulnerabilities that only appear during actual operation, such as authentication failures, session management issues, and misconfigurations.
Language independence: Because DAST works from the outside in, it is not dependent on the programming language or frameworks used to build the application. This makes it a versatile tool for testing a wide variety of applications and APIs.
Fewer false positives: DAST's reliance on real-world execution and its ability to prove that a vulnerability is exploitable often results in a lower rate of false positives compared to SAST.
Black-box testing: DAST does not require access to the application's source code, making it an excellent solution for testing third-party applications or those with proprietary code.
Disadvantages and challenges of DAST
No code visibility: A significant limitation of DAST is that it cannot pinpoint the exact line of code where a vulnerability resides. This means that while it can identify that a vulnerability exists, developers must manually examine their codebase to trace the issue back to the source.
Requires a running application: DAST can only be performed later in the SDLC once a working application is available. This can increase the cost and effort of remediation, as vulnerabilities found at this stage are more expensive to fix than those detected early.
Incomplete code coverage: DAST tools can only test the parts of an application that are executed during the scan. This means that vulnerabilities in parts of the code that are not accessed or exercised by the tool may be missed. Additionally, DAST may struggle with complex modern architectures like single-page applications (SPAs) or serverless setups.
Potential for performance impact: Without proper tuning, a comprehensive DAST scan can take a long time and affect the normal operation of the application, potentially slowing it down or even causing downtime. For this reason, many teams run DAST in staging or pre-production environments rather than live production.
Tuning and maintenance: DAST is not a "set-it-and-forget-it" solution. To be effective, DAST tools require proper configuration to handle authentication and session management. Regular tuning is necessary to minimize false positives and negatives, aligning scan parameters with the specific needs of the application.
Key steps to run DAST effectively
Implementing DAST effectively involves more than just acquiring a tool; it requires a strategic approach.
Tool selection
Choose a DAST tool that supports your application's architecture and can handle modern complexities like APIs and dynamic content. Look for features such as advanced authentication handling, automated workflows, and seamless integration with your CI/CD pipeline. Furthermore, evaluate the tool's accuracy, i.e., its ability to minimize both false positives (false alarms of vulnerabilities) and false negatives (missed vulnerabilities).
Configuration and integration
Configure the DAST tool to suit your specific needs. This includes setting up authentication credentials to scan protected areas, defining the scope of the scan to avoid third-party components, and tuning parameters to reduce noise. Embed DAST into your CI/CD pipeline so that security checks happen automatically with every code push or deployment.
Prioritization and remediation
After scans, review the results to remove false positives and prioritize identified vulnerabilities based on severity, exploitability, and potential business impact. Provide detailed reports to development teams so they can remediate issues promptly.
Continuous improvement
As vulnerabilities are identified and patched, it's crucial to add regression tests to your test suite to prevent old vulnerabilities from resurfacing. You should also provide continuous feedback to your development teams, educating them on common vulnerabilities and secure coding practices.
Complement with other methods
DAST alone will not cover everything. For a robust security posture, it's essential to complement DAST with SAST for code-level flaws, SCA for affected third-party libraries, and manual penetration testing for complex business logic issues and zero-day vulnerabilities that automated tools might overlook.
Fluid Attacks: a comprehensive approach to DAST and beyond
In the competitive landscape of AppSec solutions, Fluid Attacks offers a DAST tool that integrates seamlessly into modern development workflows. Our DAST scanner is continuously optimized to quickly assess your web and mobile applications and APIs in both production and pre-production environments.
What differentiates Fluid Attacks from many of its competitors is its holistic approach. We combine a variety of testing techniques, including DAST, SAST, SCA, cloud security posture management (CSPM), penetration testing as a service (PTaaS), secure code review (SCR), and reverse engineering (RE), all within a single, integrated solution. This provides a comprehensive security assessment that automated tools alone cannot achieve.
Fluid Attacks' DAST tool, with the use of refined attack vectors, aims to flag only unambiguously deterministic vulnerabilities, minimizing the possibility of false positives. Our scanner findings are delivered through an intuitive platform and convenient IDE extensions, making them highly practical for your development team.
Beyond just detection, we also leverage generative artificial intelligence to provide you with automated, custom fix options for specific vulnerabilities in your code, significantly easing the remediation burden. Our pentesters are also available to help your development and security teams solve questions about the most complex vulnerabilities, ensuring no issue is left unaddressed.
We can also actively check remediation success with reattacks and can even break the build in your CI/CD pipelines to prevent unsafe deployments, solidifying your security posture. Besides, our automated assessments in production environments are carried out in a safe mode without interrupting or affecting the operations of your applications.
The future of DAST: automation, AI, and comprehensive platforms
The evolution of DAST is closely tied to advancements in AI and automation. Modern DAST tools are becoming smarter and more efficient, leveraging machine learning to improve accuracy and adapt faster to new attack patterns. Automated remediation capabilities, where AI models generate and even apply secure code suggestions, are becoming more common.
However, the real future of DAST lies in its integration within a broader, unified platform. As applications become more complex and distributed, relying on multiple, siloed security tools becomes unsustainable. A comprehensive platform that combines DAST with SAST, SCA, and other methodologies provides a centralized view of security risks and a single source of truth for all vulnerabilities. This approach ensures that security is not an afterthought but an integral, automated part of the entire software development journey.
Conclusions
Dynamic application security testing is an indispensable component of a sound application security strategy. By providing a realistic, outside-in perspective of a running application, DAST uncovers runtime vulnerabilities and configuration issues that often go undetected by other methods. While it has its limitations, such as a lack of source code visibility and potential for performance impact, its strengths—including language independence and the ability to find real-world, exploitable flaws—make it a powerful prevention mechanism.
By combining DAST with complementary methods like SAST, SCA, and PTaaS, and integrating them into a mature DevSecOps pipeline, organizations can ensure a comprehensive and proactive approach to software security. Investing in DAST and related technologies not only safeguards applications but also upholds the reputation and reliability of development teams and their companies, who seek to demonstrate an unwavering commitment to excellence and security in software development.
