What is web application security testing?
Web application security testing is the process of identifying, analyzing, and fixing vulnerabilities in web applications to prevent data breaches and unauthorized access. This testing includes both automated scanning and manual evaluation of application behavior, logic flaws, configurations, and code-level issues.
As organizations increasingly rely on web applications—from customer-facing portals to internal tools—they become attractive targets for attackers looking to exploit weaknesses in these systems.
Why web applications are high-value targets
From web-based email to online shopping and banking, businesses now engage customers directly through the browser, eliminating the need for software installs or manual updates. Internally, organizations rely on custom-built web apps for functions like finance, HR, and marketing automation.
While web applications offer convenience and efficiency, their widespread use makes them a primary attack vector. According to the 2018 Verizon Data Breach Report, up to 41% of breaches in certain industries were related to web apps—and roughly half of those weren’t discovered for months. The longer attackers maintain access, the more damage they can do.
Why traditional tools aren't enough
As attackers evolve and refine their tactics, they increasingly use sophisticated methods to bypass common defenses. Even companies that follow best practices may not be safe from advanced techniques, especially when backed by well-funded attackers or organized crime groups.
Web applications are also highly complex and can confuse traditional security tools like intrusion detection systems (IDS). These tools may miss application-layer attacks entirely. That’s why web application security testing is essential—to detect the kinds of vulnerabilities that general-purpose tools often overlook.
Types of web application security testing
Different approaches to web application security testing target different layers of the application stack—from source code to runtime behavior.
Dynamic application security testing (DAST)
A DAST approach involves looking for vulnerabilities in a web app that an attacker could try to exploit. This testing method works to find which vulnerabilities an attacker could target and how they could break into the system from the outside. Dynamic application security testing tools don’t require access to the application's original source code, so testing with DAST can be done quickly and frequently.
Static application security testing (SAST)
SAST has a more inside-out approach, meaning that unlike DAST, it looks for vulnerabilities in the web application's source code. Since it requires access to the application's source code, SAST can offer a snapshot in real time of the web application's security.
Application penetration testing
Application penetration testing involves the human element. A security professional will try to imitate how an attacker might break into a web app using both their personal security know-how and a variety of penetration testing tools to find exploitable flaws. You can also outsource web application penetration testing services to a third party if you do not have the resources in-house.
Best practices for web application security testing
Test business-critical systems frequently
Any system that stores customer data—including credit card numbers, personally identifiable information (PII), or any other sensitive information—should be tested for security vulnerabilities; in fact, it's often a requirement of many government- or industry-mandated compliance guidelines. Keep this in mind when looking at the potential scope of web application security testing in your organization.
Shift security left in the SDLC
You do not want to leave security testing as a last step in software development—inevitably, vulnerabilities will be found and this can throw a big wrench into the development and maintenance processes. Bring security into the process early in the SDLC, preferably with the full involvement of your development operation (DevOps) team, to streamline response, minimize risk, and minimize any costs or time spent on remediation.
Prioritize remediation and development integration
The output of web application security testing will often be a list of items that development will need to address at some point. Security calls them vulnerabilities, but development calls them bugs. The key is to not simply drop a list of these issues into a DevOps team’s lap; instead, be sure to prioritize the vulnerabilities and fully integrate with the bug tracking system in place, in order to maximize time to remediation.
The importance of ongoing web app testing
Web application security is more critical than ever as attackers continue to evolve and target increasingly complex systems. By implementing a continuous application security testing program, organizations can strengthen their vulnerability management efforts by proactively uncovering, prioritizing, and addressing risks before attackers can exploit them. Regular testing ensures that security keeps pace with changes to your code, CI/CD pipelines, architecture, and threat landscape. Integrating security testing into your development workflows is a core principle of DevSecOps, helping teams shift left and build more secure applications from the start—especially when paired with early-stage practices like threat modeling.