web application firewall (WAF)

Charlie Yianni

min read

What is a WAF?

A WAF, or Web Application Firewall, is a security tool that sits between your web application and the internet. Its job is to filter incoming traffic and block anything suspicious - like someone trying to hack your site. Think of it like a security guard for your website, checking each visitor to make sure they’re not carrying any harmful code.

A WAF protects your application from threats like SQL injection, cross-site scripting (XSS), and other common web attacks. It does this by analyzing traffic, looking for patterns that match known attack methods, and blocking anything that looks dangerous.

How does a WAF work?

A WAF monitors and filters HTTP and HTTPS traffic. It uses a set of rules to decide whether to allow or block each request. These rules can be:

Signature-based: Matches known attack patterns
Behavior-based: Looks for unusual activity
Custom rules: Tailored to your specific application setup

When a WAF detects a dubious request it blocks it before it reaches your app.

Do you still need vulnerability scanning if you have a WAF?

Yes! While a WAF helps block attacks, it doesn’t find the underlying weaknesses in your systems. That’s where web app vulnerability scanners come in - they check your web applications for the actual security flaws that could be exploited.

A solution like Intruder performs continuous vulnerability scanning even if you’re using a WAF. In fact, if a WAF is blocking a scan, Intruder will notify you and help you resolve the issue. The platform highlights which targets are affected and gives clear instructions on how to allowlist Intruder’s scanner IPs to ensure full visibility.

So while a WAF is a great layer of protection, it’s not a replacement for vulnerability management. Together, they form a more complete defense.

Take the next step

Already have a WAF? Great - but it’s only one piece of the puzzle. Intruder gives you full visibility into your exposure, helping you spot vulnerabilities a WAF can’t block. Start your free trial and strengthen your web app defenses today.