The Ultimate Guide to DAST

Executive summary

Dynamic application security testing, or DAST, is a crucial methodology for identifying security vulnerabilities in live, running web applications by simulating real-world attack scenarios. Alongside static analysis tools, DAST has emerged as a cornerstone of modern application security, giving organizations the ability to prioritize exploitable vulnerabilities and assess the real-time security posture of their applications from an external perspective.

This comprehensive guide will help you understand how DAST tools work, how to select the product that’s right for your organization, and how to integrate DAST into your workflows to get the most out of the tool. Choosing the right DAST tool is essential for scalable security operations, yet there is still a lot of confusion around the specific features and capabilities that DAST brings to the mix alongside network vulnerability scanners, static application security testing (SAST) tools, and all the other tools making up a modern AppSec toolbox. Whether you’re responsible for securing a handful of websites or thousands of web applications and APIs (application programming interfaces), this guide should help you make DAST an effective, efficient, and fully integrated part of your security toolkit.

Where does DAST fit into an application security program?

Several factors contribute to the growing importance of DAST in modern web application security, starting with exponentially increasing application complexity. Modern web applications are hugely complex and dynamic collections of first-party and third-party code, open-source libraries, APIs, and external dependencies and services. This expands the attack surface while obscuring the internal structure, making it difficult, if not impossible, to identify all potential vulnerabilities through manual inspection or code review alone.

By providing the ability to automatically probe running applications for weaknesses on a massive scale using many of the same techniques as real-life attackers, DAST is invaluable for uncovering exploitable vulnerabilities, regardless of the underlying technologies and the origin of a security issue. Many security vulnerabilities only manifest themselves at runtime and cannot be found purely using static analysis tools that focus on the source code. As it interacts with the live application, DAST can effectively detect these runtime vulnerabilities, such as misconfigurations, authentication flaws, and issues stemming from dynamic dependencies—but also, it finds exploitable security gaps that originate from insecure coding practices.

Finally, the adoption of agile development methodologies and DevOps workflows with continuous integration has put a premium on speed and automation at all steps and tools in the software lifecycle. Security testing needs to be integrated seamlessly into these fast-paced development cycles and automated pipelines. While this can be a challenge with more basic vulnerability scanners, leading DAST solutions are specifically designed to be integrated into and automatically run in CI/CD pipelines, allowing organizations to identify and address a wider range of vulnerabilities earlier in the development process to reduce risk and costly late-stage fixes.

DAST vs. SAST: The pros and cons of dynamic vs. static analysis

DAST and SAST are both essential for building and running secure applications, but each approach is different and has its own strengths and weaknesses. SAST tools are used for static analysis and work directly on the application source code, in theory allowing for full security testing coverage of your own code.

DAST doesn’t need the source code because it works by detecting security issues in a running application, which enables it to run security checks regardless. of component origin or underlying technology, and also enables it to identify runtime vulnerabilities like misconfigurations. While it’s easy to focus on the differences and weaknesses and end up in a fruitless “which is better” debate, the rational approach is to combine SAST and DAST and play to the strengths and intended use of each to get maximum security benefits.

DAST is also called black-box testing because, by design, it performs outside-in testing without knowing or caring about the internals of an application. This technology-agnostic nature is one of the key advantages of DAST, allowing it to assess applications built in any language or framework and deployed in any architecture, making it ideal for modern, complex environments. Because it doesn’t require code access, DAST is easy to deploy and scale without extensive configuration or adjustments to your development stack. This reduces the friction commonly associated with integrating new security tools and enables organizations to begin testing quickly, leading to a faster return on investment.

The outside-in nature of DAST tools also allows them to safely simulate real-world attack scenarios, providing a realistic assessment of vulnerabilities by probing the application in real time and identifying potential weaknesses that could be exploited by attackers. Advanced DAST scanners can do double duty in application security and information security while also covering a broader attack surface than basic vulnerability scanners could, including highly dynamic single-page applications (SPAs) and API endpoints. Leading tools even come with built-in compliance reports for industry standards such as PCI DSS, HIPAA, ISO 27001, and NIST 800-53, helping CISOs maintain a good security posture and support any audit efforts.

SAST tools, on the other hand, are specifically intended to analyze source code and thus are designed to operate with and in development toolchains. Their strength is the ability to test all available source code, including code that hasn’t yet been integrated into a running application or that is present in the codebase but not executed in a specific app or scenario. Because it works directly on the code, SAST can pinpoint issues down to the line of code and statement. When integrated and used from the earliest stages of development, SAST serves as the first line of defense to catch security flaws as quickly as possible.

The quality of results for both DAST and SAST can vary widely depending on the specific product, but in general, SAST tools are by design prone to false alarms (false positives) because they analyze code in isolation, without knowing the developer’s intention or the context of how the application behaves at runtime. As a result, SAST is famed for flooding developers with false or even just non-actionable warnings, leading to alert fatigue and creating the risk of real vulnerabilities slipping through hidden in the noise.

In contrast, advanced DAST solutions have largely solved this problem through automated vulnerability confirmation (like Invicti’s proof-based scanning) to ensure that exploitable issues are flagged and reported as such, providing security teams and developers alike with clear, actionable insights for remediation.

How DAST works: A deep dive into dynamic analysis and the testing process

DAST tools typically go through a multi-stage process to find and report vulnerabilities, though which steps a specific tool covers and how well it does them depends heavily on the type and maturity of the specific product. Basic vulnerability scanners are designed to only cover the vulnerability testing step, so the process outlined below follows Invicti’s comprehensive approach to a DAST-based application security testing program and not all critical steps will be covered by less advanced tools.

Discovery, prioritization, and crawling

Before actual testing can begin, you need to know which targets (sites, apps, or APIs) you need to test and which specific URLs and parameters the scanner will be targeting. This requires asset discovery followed by manual setup to enter known URLs and API specs. For sites and apps, this is followed by the tool crawling the application to understand its structure and attack surface. You can think of the crawling process as emulating a user interacting with all accessible elements of a site: following links, clicking buttons, submitting forms, etc.

Advanced DAST solutions have a fully embedded browser engine to correctly and completely crawl, and later test any website or application that can run in a modern browser. They should support industry-standard authentication mechanisms, including OAuth, so that they can access and test pages and features that require login. Only a handful of tools can also process API definition documents, such as OpenAPI (Swagger) specifications, allowing them to map out and test API endpoints alongside user-accessible site pages.

Once the websites and applications for testing have been identified and mapped out, the DAST tool can start actual security testing. It does this by sending specially crafted requests that include simulated attack payloads to the identified entry points (input fields, parameters, etc.) of the application. These payloads are designed to expose and (for more advanced tools) safely exploit various security flaws in a website or application. Common vulnerabilities detected by DAST include:

• SQL injection: Malicious database commands are included in unsanitized application inputs.
• Cross-site scripting (XSS): Malicious scripts are injected into an application to manipulate site content or steal data.
• Server-side request forgery (SSRF): Attackers are able to send requests from or via a vulnerable server, potentially accessing internal systems and sensitive information.
• Insecure authentication: Access to an application or API is weakly secured, allowing attackers to bypass authentication.
• Misconfigured HTTP headers: Best-practice security headers such as Content Security Policy (CSP) or HTTP Strict Transport Security (HSTS) are missing or incorrectly configured, greatly decreasing the overall level of security.

The number, scope, and quality of available security checks vary widely depending on the product, so be sure to seek out detailed technical information when evaluating tools. Also, be wary of sweeping claims like “our tool finds all the OWASP Top 10” because there is no DAST tool in the world that can do that (especially since the 2021 edition, where the top 10 went away from listing specific vulnerabilities in favor or broader risk categories).

A vital distinction to make is between security weaknesses discovered in the application itself (CWEs) and known vulnerabilities in products and components (CVEs). Both are commonly called “vulnerabilities” but are two different concepts. Only DAST tools can discover previously unknown vulnerabilities, and that is their primary purpose. For example, by successfully performing SQL injection on an application, a DAST tool discovers an SQL injection vulnerability—often one that’s never been reported before, if it’s a new application or one still in development. Vulnerable technologies and components reported as CVEs can be discovered by advanced DAST tools as well as by network security scanners and are identified by comparing scan data with public vulnerability databases such as the NVD.

Vulnerability prioritization and remediation

Throughout the testing process, a DAST tool continuously monitors application reactions to its simulated attacks, looking for values or behaviors that may indicate a vulnerability. As mentioned above, mature DAST solutions go beyond simple pattern matching and are often able to safely and conclusively verify if a vulnerability is exploitable. Examples may include injecting a read-only database command and extracting a unique value from the database server to prove that an SQL injection vulnerability exists. Because these confirmed results are proven to be exploitable, they cannot be false positives and should be prioritized for remediation.

Each vulnerability identified during scanning is reported as a scan result. Again, DAST tools vary widely on the level of detail provided in vulnerability reports, with only the more advanced solutions generating detailed and actionable reports that include sufficient technical details to isolate and fix the root cause. A good vulnerability report should include:

• A clear description of the vulnerability and its potential impact
• The estimated severity level (typically Critical, High, Medium, or Low)
• The location of the vulnerability (URL, parameter, and any additional information)
• The technical details of the vulnerability, such as the attack payload used and the HTTP request and response
• Remediation advice for developers to fix the vulnerability

A detailed, actionable, and trustworthy vulnerability report provides developers with clear steps to reproduce and fix issues, accelerating remediation. Accurate location information along with initial prioritization by the tool helps teams organize their response to address the most critical assets and issues first in a proactive manner. The quality of DAST scan results and of the way they are reported makes the difference between wrestling with an endless backlog of potential issues and working through clear tickets that result in immediate and measurable security improvements.

How to choose the right DAST tool for your organization

From open-source tools to bundled products and fully dedicated DAST platforms, there’s a wide variety of DAST solutions out there at very different capability levels and price points. It’s pretty much accepted that any application security program needs to incorporate a DAST tool (and there are even some regulatory requirements to use one), but selecting the specific tool that’s right for your organization requires careful consideration of several factors.

Accuracy and depth of testing

Building a scanner is easy. Building an accurate scanner is extremely hard. To get useful results that translate into security improvements, look for DAST tools that are equipped to handle the complexities of modern web applications, including single-page applications (SPAs) built with JavaScript frameworks like React, Angular, and Vue.js. Basic scanners that expect to deal with mostly static web pages can miss entire sections of apps and sites that are rendered and modified dynamically by manipulating the document object model (DOM) of the page.

Leading DAST solutions incorporate a full browser engine to load and test any page in its entirety, including testing for vulnerabilities such as DOM-based XSS. Also, be on the lookout for second-order and out-of-band vulnerability detection.

Nearly all applications and APIs require authentication to access at least some of their functionality. To test deeper than only a handful of public pages, any serious DAST solution should support authenticated scanning to ensure it can also access and examine restricted pages. While any tool can usually be made to authenticate in a manual process, routine automated scans require support for industry-standard authentication mechanisms, including OAuth, to ensure that, once set up, the scanner doesn’t require manual intervention.

Authenticated scanning is vital to avoid a false sense of security that arises when you’ve run a scan and found no vulnerabilities but, in reality, a significant portion of your application’s attack surface remains untested and potentially at risk.

A key challenge with any automated testing tool is the potential for false positives—reported vulnerabilities that are not actual vulnerabilities. The risk of false positives in scan results can undermine all efforts to build an automated security testing process because false alarms cannot be processed automatically without flooding developers with junk tickets, requiring manual validation to weed out.

Look for DAST tools that provide evidence-based vulnerability confirmation to clearly indicate which vulnerabilities are exploitable and cannot be false positives. Invicti DAST achieves this through accurate and reliable proof-based scanning.

SDLC integration and automation

When scanning applications that you’re developing in-house, you want to balance security with efficiency to ensure that security testing isn’t getting in the way of development deadlines. Especially in fast-paced and heavily automated DevOps environments, integrating security testing directly into your development pipeline is crucial, so look for DAST solutions that integrate with popular CI/CD platforms like Jenkins and industry-standard issue trackers such as Jira.

Assuming the tool delivers reliable results, workflow integration allows automated DAST to run as part of the build and deployment process, enabling your teams to catch more vulnerabilities early and prevent them from reaching production environments.

DevOps relies on automation to maximize development efficiency while minimizing manual intervention. To add security into the mix and successfully build a DevSecOps process, look for DAST products that, in addition to integration, also provide a high degree of automation in both pre-production and production testing. Leading solutions can:

• Trigger predefined scans at specified stages of the pipeline (e.g. upon build submission)
• Schedule automated security scans at regular intervals and during specified time windows
• Trigger alerts and notifications based on predefined criteria (e.g. when a high or critical severity issue is found)
• Automatically generate summary reports and send them to specified stakeholders

Automating these tasks reduces manual effort, minimizes the risk of human error, and ensures consistent security testing across your applications.

Vendor support and product maturity

Every DAST tool requires proper setup and fine-tuning to adapt to the unique requirements of each organization and its application environment, ensuring accurate detection while minimizing noise. Though leading solutions will deliver some results right out of the box even with suboptimal settings, technical support and onboarding assistance from the vendor are essential to maximize scan coverage, accuracy, and performance, set up efficient workflows, and start getting real value quickly. In fact, a common complaint from users of free or bundled DAST tools is that they are left on their own to figure out configuration issues, spending hours of their valuable time setting up and maintaining a tool that is ostensibly low-cost but getting little to no security benefit. Before selecting a DAST tool, be sure to check which onboarding and support options are available from your vendor of choice.

The application security market is now crowded with vendors, making it essential to research a vendor’s history, reputation, experience, and commitment to providing high-quality products and support. Look for vendors with a proven track record in the application security domain, a strong customer base, and a commitment not only to innovation and ongoing product development but also to security education. With DAST in particular, building and refining your own scan engine takes many years, resulting in many companies actually offering tweaked and repackaged open-source scanners such as ZAP rather than an original product.

Related to this is the imperative of keeping your DAST updated with all the latest vulnerability data and attack techniques. A good DAST tool needs to identify CVEs and also incorporate security checks that reflect the current state of the art in offensive security. Make sure the DAST tool you choose is actively maintained and updated to address new threats and developments. Frequent updates, new security checks, new features, and prompt responses to security emergencies are all good indicators of a vendor’s commitment to keeping their product effective and relevant.

API security testing

APIs are the “underwater” part of most modern web applications, providing direct access to data and functionality but remaining unseen to most users. While running security checks on an application’s API endpoints may technically seem similar to testing pages and parameters accessible through a GUI, very few DAST tools are advanced enough to do it accurately. With APIs becoming prime targets for attackers, it’s crucial to ensure you have a DAST solution that has dedicated features for automated API security testing.

To systematically test APIs for vulnerabilities, a DAST tool should provide support for popular API architectures—at a minimum REST (as the most popular), but SOAP, GraphQL, and gRPC should also make the list. For each architecture, the solution also needs to support all the popular specification formats to ensure you can import API specs and test endpoints regardless of the approach used by your dev teams. As an example, Invicti currently supports no less than 16 types of API specification files, including popular proxy formats to work from captured traffic when official documentation is not available.

Most business APIs are (or should be) only accessible to authorized users, so solid support for modern authentication methods is another must-have for any DAST used for automated API security testing. Unlike with GUI applications, where an unauthenticated scan may be incomplete but at least it will run, authenticated scanning is non-negotiable when it comes to APIs. Invicti DAST provides support for basic HTTP authentication, JSON Web Tokens (JWTs), and OAuth2—the latter giving you the ability to scan in single sign-on environments.

Centralized visibility into your security posture

In the DAST market, what sets comprehensive solutions apart from basic scanners is what they can do for your cybersecurity program, so platform maturity is a crucial item on any DAST buyer’s checklist. A simple scanner runs a scan and returns some results, and the rest is up to you. A modern DAST solution, on the other hand, can act as a central hub for vulnerability testing and attack surface management. Its technology-agnostic nature makes DAST the ideal platform for connecting and centralizing additional testing methodologies, such as SAST, IAST (interactive application security testing), dynamic and static SCA (software composition analysis), and API security. With DAST acting as your external attack surface umbrella, you can dive deeper where necessary while maintaining centralized visibility into your realistic application security posture.

You can’t test or protect what you don’t know about, so integrated asset discovery features should also be a part of any serious DAST platform, covering websites, applications, and APIs. Especially for larger organizations with extensive application environments and infrastructures, automated discovery helps to find any exposed assets that have evaded inventory efforts, letting you cover them with vulnerability testing where required. In a large environment, prioritization can be hard, so Invicti DAST includes Predictive Risk Scoring to show you which sites and apps are most likely to be vulnerable before you even run the first scan. Added to that is API discovery—an Invicti feature that’s unique among DAST platforms and helps you keep tabs on your entire web attack surface, APIs included.

Reporting is a vital part of any application security program to communicate the right information to different stakeholders and help track compliance or remediation progress at different levels. For example, reports for developers need to include detailed technical information and remediation guidance for specific vulnerabilities, while a monthly security posture report for an executive audience needs to focus more on high-level trends and observations. Look for solutions that feature built-in reports for common compliance requirements such as PCI DSS, HIPAA, and ISO 27001 while also letting you define custom reports to match your specific needs. Trend reports and dashboards can also be very useful for monitoring the progress of security efforts in the longer term and identifying areas for improvement.

Best practices for implementing DAST

There’s a world of difference between getting any security tool and getting value from it, and this is especially true of DAST. To round out this guide, here are a few best practices for successfully integrating a DAST solution into your application security program and development workflows.

• Define clear DAST objectives: Before deploying a DAST solution, clearly define your security goals and know where DAST fits into your overall security strategy. DAST is flexible and can cover many bases, but what specifically are you trying to achieve with the current deployment? Possible goals include meeting compliance requirements, improving the security of internally developed applications, and getting a better grip on your overall web application security posture.
• Integrate DAST into your SDLC to build DevSecOps: When you’re building and running your own applications, especially in a DevOps, building DAST into your software development lifecycle (SDLC) can greatly cut down on manual security tasks and reduce the number of vulnerabilities that make it into staging and production. SDLC integration typically means running automated scans in CI/CD pipelines (often triggered by commits) and running periodic scheduled scans on development and staging builds.
• Start with a phased approach: Trying to scan everything at once can be overwhelming, especially when first implementing DAST on a large scale, so a proactive and phased approach can be more practical. Begin with your business-critical applications and those you know to be at risk (Predictive Risk Scoring can be invaluable at this stage). As you reduce the vulnerability backlog and refine your processes, slowly expand the scope of DAST testing to include other applications, eventually carefully incorporating scheduled scans of production applications into your DevOps workflow.
• Gradually fine-tune your scanner configuration: Any decent DAST tool should offer a wide range of options to customize the scan process for your application environment and security requirements. As you learn how the scanner interacts with your scan targets, you can exclude specific security checks and URLs to improve performance or cut down on unneeded results, or customize checks to better match your environment. Fine-tuning should include scan authentication to maximize coverage for your specific auth flows, while performance can be gradually optimized to balance scan depth and speed, especially when working with limited scan windows.
• Build DAST into your vulnerability management process: Use a centralized system for tracking all vulnerabilities found by DAST, whether it’s a dedicated vulnerability management system, management features in the tool itself, or integration with an existing issue-tracking system such as Jira. Prioritize vulnerabilities based on technical severity, exploitability, and the potential business impact and have an automated process to assign them as tickets for remediation. Define and review vulnerability management metrics to track progress, identify trends, and measure the effectiveness of your security program.

Conclusion: DAST is not a checkbox but a cornerstone of application security

DAST scanning is now an explicit compliance requirement for many organizations, leading some to treat it as yet another checkbox. This isn’t helped by vendors who specialize in another area of application security and deliberately downplay the significance of DAST relative to their own flagship approach, sometimes even bundling a mediocre DAST just to help a customer tick that box. In reality, using a good DAST tool is a non-negotiable requirement for any effective application security program—but that’s not all.

When implemented correctly and effectively, a serious DAST solution can go far beyond vulnerability scanning to become a cornerstone of your whole application security program. By combining all the benefits that comprehensive DAST brings to the table, you can improve software security, streamline compliance, remove security testing bottlenecks, and help finally make security a routine aspect of software quality.

And on top of that, because it’s the only application security testing tool you can use for both AppSec and InfoSec, DAST gives you double the bang for your buck.

More than a box to tick: Meet the real DAST

Check out the DAST checklist