Author: Kateryna Ivanenko, Invicti Brand Manager
In the field of web security, there is a widespread statement: “We have WAF installed — that is enough.” However, this point of view is faulty and potentially dangerous. Web Application Firewall (WAF) and web scanners are solutions that complement each other, and not interchangeable tools. This article examines the key differences between them and explains why even the most modern WAF cannot replace a DAST scanner.
What does a WAF do?
A WAF analyzes HTTP(S) traffic between a user and a website. Its main task is to stop potentially malicious requests. It does this by inspecting the request headers, the request body, and other parameters based on predefined rules or signatures.
What does a DAST scanner do?
DAST (Dynamic Application Security Testing) analyzes a web application from the outside, simulating the behavior of an attacker — sends HTTP requests, analyzes responses, checks whether vulnerabilities can be exploited. Unlike WAFs, scanners such as Invicti (formerly Netsparker):
- Proactively detect vulnerabilities in websites and APIs, including misconfigurations.
- Integrate into CI/CD, allowing specialists to detect flaws even before release.
- Generate reports for teams, including recommendations for eliminating vulnerabilities.
Proactive vs. reactive approach
The key difference between these tools is their opposite methods of work. The main function of a WAF is to block suspicious actions according to specified rules, that is, at the moment of the attack. Web scanners, in turn, detect vulnerabilities before an attacker can use them.
That is, a WAF is a “shield”, but not a “diagnostic”. It does not guarantee that the application does not have vulnerabilities that can be exploited, for example, when bypassing a firewall, and at best only masks them.
A typical scenario of false security
For example, some web application has a SQL injection vulnerability in one of the API parameters. A WAF may not recognize the attack if the payload is obfuscated. An attacker with sufficient technical knowledge can bypass the firewall and achieve their goal. And if the vulnerability had been detected by a web scanner, ideally it would have been eliminated at the development stage.
A WAF is only a barrier. If the application has a serious vulnerability, it can be exploited with a bypass, especially if the WAF policies are configured minimally to avoid false positives.
Web scanners are essential for compliance
Many regulations (PCI DSS, ISO 27001, OWASP ASVS) explicitly require active scanning of web resources for vulnerabilities. Installing a WAF does not exempt from this obligation.
Conclusion: synergy instead of choice
The ideal option is to use both a web scanner and a WAF. A firewall is an important component of protection, but it does not replace a systemic approach to web security. Invicti allows companies to conduct deep analysis of websites, confirm the existence of vulnerabilities and integrate security into the development process. Combined with a WAF, this is a powerful defense.
