How WAF Works?

What Is a WAF?

A Web Application Firewall (WAF) acts as a shield between web applications and the internet, protecting them from various web-based attacks. Unlike traditional network firewalls that operate at lower network layers (like Layers 3 and 4), a WAF specifically focuses on the application layer (Layer 7) of the OSI model, where web applications reside and communicate using HTTP/HTTPS.

Step-by-Step Process: How WAF Works?

1. Intercept Incoming Request: The WAF sits between the internet and your web application. Every HTTP or HTTPS request from a user first goes through the WAF. It acts like a checkpoint, catching all traffic before it can touch your server.

2. Analyze Request Content: The WAF deconstructs the incoming request to scrutinize every piece of data. This isn't just a simple header check; it's a deep, granular inspection. The WAF parses the entire request, looking at things like:

• HTTP Headers
• URL/URI
• Query Strings
• HTTP Body
• Cookies
• File Uploads

It checks for strange patterns or data that could signal an attack.

3. Match Against Security Rules: It compares the request against known attack signatures and rule sets (like the OWASP Top 10 threats). This includes detecting:

• SQL Injection (like OR 1=1, UNION SELECT)
• Cross-Site Scripting (XSS)
• File inclusion attacks
• Command Injection
• Protocol violations, and more

4. Decide on Action:  This is where the WAF's policies come into play. It has to make a quick decision about what to do with the request based on the analysis.

• Allow: If the request passes all the security checks, the WAF forwards it to the web application server for processing.
• Block: If the request is a clear and immediate threat (e.g., it contains a well-known SQL injection signature), the WAF will drop the request and send an error response back to the client.
• Challenge: For suspicious but not outright malicious requests, the WAF might issue a challenge like a CAPTCHA to verify if the client is a human or a bot.
• Alert Only (Monitor Mode): In this mode, the WAF allows all traffic to pass through but logs every potential threat.

5. Send Response: If the request is allowed, it's passed on to your web server to be processed normally. The user sees no difference in speed or experience.

6. Log and Alert: The WAF logs all activity, especially anything it blocks or flags. It can send alerts, generate reports, and give admins visibility into potential threats in real time.

WAF Deployment Options

There are three common WAF deployment models:

• Network-Based (Hardware Appliance): High performance, low latency, physical setup.
• Host-Based (Software/Agent): Installed on the server, customizable but resource-heavy.
• Cloud-Based (SaaS): Easy to deploy, scalable, and vendor-managed (e.g., AWS WAF, Cloudflare).

In conclusion, the WAF acts as an intelligent, vigilant gatekeeper, inspecting every interaction with your web application in a fraction of a second to ensure security without impacting performance for legitimate users.

How Can InfosecTrain Help?

InfosecTrain helps you understand WAF through expert-led courses like AWAPT training and CSSLP training, offering hands-on labs, real-world attack simulations, and deep dives into application security, enabling you to configure, test, and integrate WAFs effectively into security frameworks.