Not Just DDoS: Common Attacks a WAF Can Prevent 

Imagine your website or mobile app is a cozy house with an open door. You welcome every guest—but some of them may come with bad intentions. One might try to crack the safe or steal documents, while others might storm in with a crowd of a thousand and turn on all the taps to flood the place.

In this story, the Web Application Firewall (WAF) is the security guard at the door, checking everyone who wants to come inside. But what exactly does this guard protect you from? And can it really hold back the full force of a DDoS attack? Let’s break it down.

What is a WAF?

A Web Application Firewall (WAF) is a security layer that inspects incoming traffic and blocks potentially dangerous requests before they reach your application. It operates strictly at the application layer (Layer 7) of the OSI model. In other words, it’s positioned at the very front—analyzing the traffic “at the door” before the application processes any data.

In practice, a WAF scans everything available in HTTP/HTTPS and other Layer 7 protocols. If it detects anything suspicious—whether it’s in the request body, headers, or URI—it blocks the request immediately.

Learn more: What is a WAF and How It Works

What counts as “suspicious”? Typically, it refers to patterns that resemble known vulnerabilities. Think of the OWASP Top 10 list—that’s a good place to start.

What Does WAF Protect Against?

A Web Application Firewall (WAF) is one of the most widely used tools in cybersecurity—and for good reason. It helps protect web applications from many types of cyberattacks. Here are some of the most common threats a WAF can defend against:

• SQL Injection: One of the most widespread attack types targeting websites and apps. The idea is simple: an attacker injects malicious SQL code into a request to gain access to view or manipulate the database.
• XSS (Cross-Site Scripting):  Another common attack where the attacker injects harmful scripts, typically JavaScript, into a webpage. These scripts can steal user data, hijack sessions, or carry out unauthorized actions.
• File Inclusion (LFI/RFI):
  • LFI (Local File Inclusion): Allows attackers to execute files stored on the local server, which can expose sensitive configuration data.
  • RFI (Remote File Inclusion): Loads a file from a remote server, enabling the attacker to run malicious code on the application.
    
• RCE (Remote Code Execution): Considered one of the most critical web threats by OWASP. This allows attackers to remotely execute arbitrary code on a compromised server or system, potentially taking full control.
• PHP Injection: A method of compromising PHP-based websites. The attacker tries to execute unauthorized PHP code, which in extreme cases may grant full server access.
• Automated Actions: This includes brute-forcing login credentials, trying out promo codes, or auto-adding items to carts to block real purchases. 
• Bots: Used for scanning vulnerabilities, scraping content, or generating large volumes of traffic. WAFs help detect and block harmful bots while allowing legitimate traffic through.
• Brute Force Attacks: An attacker attempts to guess valid session IDs or passwords to hijack user accounts or gain unauthorized access.

These are just some of the most common attacks a WAF can help prevent. But there’s one more major question: can a WAF stop DDoS attacks? That’s worth discussing separately.

WAF vs. DDoS: What’s the Deal?

“Does a Web Application Firewall protect against DDoS attacks?” It’s one of the most common questions we hear—and the answer is: yes and no.

Yes—if the DDoS attack occurs at the application layer (Layer 7). For example, if attackers simulate real user behavior or send an overwhelming number of requests to a login form or API endpoint, a WAF can help. Because it operates at L7, it’s capable of identifying and filtering such behavior in real time.

But if the attack is more brute-force in nature—flooding the network with massive amounts of traffic at the transport or network layer (L3/L4)—a WAF alone won’t help. These types of attacks hit long before traffic even reaches your application. To counter them, you’ll need dedicated anti-DDoS services that can detect and mitigate threats at earlier stages of the traffic flow.

Put simply, the WAF is a specialist in analyzing content, not handling volume. It’s effective against targeted, smaller-scale L7 attacks—but not designed to absorb large-scale floods.

Read also: L7 DDoS Protection Guide: How to Stop Application Layer Attacks

When Do You Actually Need a WAF?

If your business depends on a website or web application, the answer is simple: you need a WAF.

It helps you avoid downtime, preserve your brand reputation, protect customer data, and reduce the risk of security incidents that could lead to real financial loss.

While a WAF isn’t a silver bullet, it plays a critical role in detecting and blocking common attacks like SQL injections, bot activity, and malicious payloads. And even though it doesn’t replace full DDoS protection, it’s a key part of a layered security strategy.

In Conclusion

A WAF alone may not hold back a massive wave of traffic—but it will definitely stop someone trying to slip in unnoticed with malicious intent. It’s not your entire security system, but it’s your gatekeeper—checking IDs, scanning bags, and quietly keeping your digital storefront safe.

For broader protection, we always recommend pairing a WAF with a dedicated anti-DDoS solution for web applications. That way, you’re covered from both sides—smart filtering at the door and traffic mitigation at the edge. And when the storm comes, your digital house will stand strong.