What Is a WAF and What Does It Do?

It’s easy to assume that only large corporations are targeted by cyberattacks, but that’s not the case. Small business websites are vulnerable too, often more so because they typically lack robust cybersecurity defenses. In fact, more than 50% of all internet traffic is made up of bots, and not all of them are benign. While some bots (like search engine crawlers) are helpful, about 37% consist of bad bots that are designed to probe for weaknesses, steal data, or take down your site. That’s where a WAF comes in. It inspects every visitor and data request coming to your website, automatically blocking those that show signs of malicious intent.

Let’s explore what a WAF is, how it works, why small businesses should use one, and what types are available—so you can take the first step toward securing your site.

WAF meaning

As a website owner, you may have come across a certain three-letter term and wondered to yourself, “What is a WAF?” or “What does WAF mean?” Think of it this way: if your website infrastructure is a house, the web application firewall (WAF) acts like a fence, helping to deter unwanted visitors. WAFs monitor two-way HTTP or web traffic and defend an application against harmful cyberattacks threatening the website.

A WAF is a filter that protects your web application against a plethora of different attacks. These attacks may attempt to pull sensitive data from your site, which is an issue if you routinely work with customers or exchange details such as credit card information. What is a WAF’s advantage compared to other types of cybersecurity measures? WAFs typically work within a fraction of a second, inspecting incoming HTTP traffic and filtering out malicious traffic or files that may be harmful, using a series of security rules, often referred to as “policies.”

So why is a WAF needed?” Well, an average website could face thousands of attacks per day. All it takes is one successful attempt to completely bypass your security measures and thoroughly corrupt your site. However, all of this can be easily avoided by employing a WAF, along with other cybersecurity measures, to automatically defend your site from attacks.

What does a WAF do exactly?

A WAF filters, monitors, and blocks harmful traffic before it can reach your web application or API. Unlike network firewalls, which guard against common attacks like port scans or brute-force login attempts, this security tool focuses on web-based threats that can compromise user data or disrupt your services. Key threats a WAF defends against include:

• Malicious bots that scrape data, look for vulnerabilities, or attempt brute force attacks

• Malware file uploads or unauthorized code changes

• Distributed Denial-of-Service or DDoS attacks meant to overwhelm your site

• Application-layer attacks like SQL injection and cross-site scripting (XSS)
  

WAFs also help businesses stay compliant with regulations like PCI DSS, which mandates the protection of cardholder data. With the threat landscape evolving constantly, WAFs often use regularly updated threat intelligence and rule sets to stay ahead of attackers.

In addition to these core protections, robust WAFs are designed to defend against a wide range of threats, including those listed in the OWASP Top 10—a standard awareness document that outlines the most critical web application security risks, such as broken authentication, security misconfigurations, and sensitive data exposure. Ensuring your WAF covers these vulnerabilities is essential to maintaining comprehensive security.

Importance of encrypting data

While a WAF is excellent at filtering out dangerous traffic, it does not encrypt sensitive data being transmitted between users and your site. Information like passwords, credit card details, and Social Security numbers is still at risk unless encrypted with HTTPS.

To fully protect your users and endpoints, your WAF should be compatible with an SSL certificate and support HTTPS connections. This ensures that any data entered into your forms is encrypted in transit, adding another crucial layer of security to your site.

How does a WAF work?

A WAF protects a website by using a set of security policies or rules that inspect each HTTP request sent to your web server. These rules may identify and block requests that match known attack vectors or exhibit suspicious behavior.

There are three primary methods a WAF may use to assess traffic:

• Whitelisting: Only pre-approved sources or behaviors are allowed.

• Blacklisting: Known bad actors or suspicious behaviors are blocked.

• Hybrid: A flexible approach combining both strategies.
  

Most WAFs use real-time analytics to examine request headers, URLs, cookies, and payloads. If something looks off—like an attempt to inject SQL commands into a login form—the WAF denies the request instantly. This protects your application before the server ever sees the threat.

However, it’s important to know that WAFs only monitor traffic routed through your domain name. If someone tries to bypass the firewall by accessing your server directly via its IP address, that traffic could go unfiltered. To prevent this, configure your server (such as through a .htaccess file) to block direct IP access and allow only traffic passed through the WAF.

Types of WAFs

There are three types of web application firewalls: hardware-based, software-based, and cloud-based. Every type will protect your site infrastructure, though they may do so in different ways. The main differences between them are in the implementation and storage procedures.

• Hardware-based: A hardware-based WAF is installed locally on the computer’s hardware. This type of WAF is quick, agile, and effective, but may cost slightly more to install. It also takes up storage space on the hosting device, so you’ll need to consider available computer memory.

• Software-based: This type of WAF is fully integrated into an application’s software, allowing you greater customization. This option is mid-priced compared to the other options. Implementation can be tricky depending on the application you’re working with, but once it’s installed, all that’s left to do is routine maintenance.

• Cloud-based: Cloud-based WAFs are the quickest type to install and come in at the lowest price point. One of the main advantages cloud-based WAFs provide is that they are easy to tune up and update. This option is user-friendly, though users may be less familiar with specific features and controls since they are not running the program directly.

When it comes to each different type, what is a WAF’s biggest upside—and consequently, the downside? There are pros and cons accompanying every type of WAF, depending on the kind of web user you are and how much time and money you want to dedicate to maintenance. But the fact remains that no matter which option you choose, your website will benefit from greater protection against automated attacks.

Why small businesses are targeted

Cybercriminals often view small businesses as low-hanging fruit. Why? Because while they still handle sensitive data like credit card numbers, email addresses, and login credentials, they often don’t have dedicated security teams or the budget for enterprise-grade protection. That makes them prime targets for data theft, ransomware, and phishing campaigns.

Even more concerning, small businesses can be used as entry points into larger networks. A now-infamous example: attackers who breached Target’s customer data in 2013 did so through a small HVAC vendor with weaker security protocols. If your business has vendor relationships with larger organizations, your website could be the backdoor hackers are looking for.

Investing in a WAF isn’t just about protecting your website—it’s about protecting your customers, your partners, and your business reputation.

Mitigate cyberattacks with SiteLock’s WAF

The average website faces a cyberattack every 39 seconds, and it only takes one to inflict serious damage. A WAF functions as a critical, proactive security solution that can stop these threats before they start, without requiring constant manual oversight.

Whether you're just launching your site or already attracting traffic, now is the time to strengthen your cybersecurity posture.

Ready to secure your site? Don’t wait for an attack to take action. Protect your business today with SiteLock’s powerful WAF solutions.