Table of contents
What is a WAF?What does a WAF protect against?Key functionalitiesHow a WAF fitsWAF deployment optionsWhy WAFs matter for modern websitesDevSecOps and complianceFAQsGetting startedHosting optionsAdditional resources
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What is a web application firewall (WAF)?

Cyberattacks don’t just target servers and networks—they often go straight for the application layer. That means your login forms, shopping carts, comment boxes, and search fields are all potential attack surfaces. A traditional firewall won’t catch those threats, but a web application firewall (WAF) will.

Let’s break down what a WAF is, how it works, and why it’s such an essential part of modern website security.

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What is a WAF?

A web application firewall (WAF) is a security tool that sits between your website and the internet. It inspects incoming traffic and blocks anything that looks suspicious or dangerous before it ever reaches your application.

Unlike traditional firewalls that look at IP addresses and network ports, a WAF analyzes actual web requests, like form submissions, URLs, headers, and cookies. That makes it uniquely suited to catch attacks that target websites specifically.

What does a WAF protect against?

WAFs specialize in detecting and blocking threats at the application layer (layer 7 of the OSI model). That includes attacks designed to trick your app into revealing data, executing malicious code, or overloading your resources.

Common attacks that a WAF defends against include:

  • SQL injection: When an attacker tries to send SQL commands through a form or URL to access or alter your database.
  • Cross-site scripting (XSS): When malicious scripts are injected into a web page and executed in another user’s browser
  • File inclusion: When attackers try to load remote or local files into your application to execute malicious code.
  • Cookie poisoning: When someone tampers with cookie data to gain unauthorized access.
  • Cross-site request forgery (CSRF): When a logged-in user is tricked into performing actions without their knowledge.
  • Layer 7 DDoS attacks: These flood your app with fake HTTP requests to overwhelm your backend.

Many WAFs also block known bad bots, enforce rate limiting to stop brute-force login attempts, and restrict access based on IP reputation or geolocation.

Key functionalities of a WAF

To identify and stop malicious traffic, WAFs use several techniques, often layered together:

  • Signature-based detection: Recognizes known patterns of attacks, like specific strings used in SQL injection.
  • Anomaly detection: Flags traffic that behaves unusually, such as a user submitting thousands of login attempts in a few seconds.
  • Behavioral analysis: Learns what “normal” user behavior looks like and blocks traffic that deviates sharply.
  • Bot protection: Identifies and blocks bots that scrape content, test stolen credentials, or attempt to overload your forms.
  • Rate limiting: Limits how many requests an individual IP address can make in a given time frame.
  • Geo-blocking and IP filtering: Restricts traffic from high-risk regions or known bad IP addresses.

How a WAF fits into a layered security strategy

A WAF isn’t a replacement for other security tools. Rather, it’s part of a larger defense system.

  • Network firewalls protect against attacks at layers 3 and 4 of the OSI model (think IP addresses, ports, and protocols).
  • WAFs operate at layer 7 (the application layer), where user input, HTTP requests, and web sessions live.

This makes WAFs a critical second line of defense. If an attacker slips past a network firewall or enters through a browser, the WAF can still catch them before they reach your app’s core logic.

WAF deployment options

There are three primary ways to deploy a WAF, depending on your infrastructure and how much control or ease of use you need.

1. Cloud-based WAFs

A cloud-based WAF is hosted and managed by a third-party provider. Your site’s DNS or traffic routes through their network, where the WAF filters out malicious traffic before sending clean requests to your server.

  • Examples: Cloudflare, AWS WAF, Akamai
  • Benefits: Easy to set up, no maintenance required, scales with traffic
  • Best for: Websites and ecommerce stores that want quick protection without server complexity

2. Appliance-based WAFs

These are physical or virtual devices that live in your data center or private cloud. They act as a gateway for your web traffic and are fully under your control.

  • Benefits: Full control and customization, excellent for sensitive or regulated environments
  • Drawbacks: Expensive, complex to manage, needs skilled staff
  • Best for: Large enterprises or government agencies with strict compliance needs

3. Software-based WAFs (including host-based WAFs)

A software-based WAF is installed directly on a server. It could be the same server that runs your application (host-based), or a dedicated sidecar server within your environment.

Host-based WAFs

A host-based WAF is a firewall that runs on the same machine as the web application itself. It’s the most common type of software-based WAF. A host-based WAF monitors local HTTP traffic, inspects requests before they reach the application code, and can log or block threats in real time.

  • Examples: ModSecurity with Apache or NGINX
  • Benefits: Deep integration, access to server logs, customizable rules
  • Drawbacks: Shares resources with the application, may impact performance if not tuned
  • Best for: Developers and DevOps teams with hands-on server access

Host-based WAFs are a great fit for those using VPS, dedicated servers, or containers where they control the application stack.

Why WAFs matter for modern websites

Without a WAF, your application is wide open to common exploits that automated bots and attackers try every day.

A WAF helps:

  • Protect customer data from theft or leakage
  • Prevent fraud by blocking malicious bots and abuse of login forms
  • Ensure uptime by mitigating targeted DDoS attacks at the application layer
  • Support compliance with security standards like PCI DSS, HIPAA, or GDPR
  • Reduce costs by lowering the risk of security incidents and breaches

If your site processes logins, credit cards, or any kind of personal data, a WAF is no longer optional.

How WAFs support DevSecOps and compliance

WAFs can be part of a modern DevSecOps workflow by integrating with cloud infrastructure and automation tools:

  • CI/CD integration: Some WAFs can deploy rules automatically as part of your app deployment process.
  • Real-time alerts: WAFs can send alerts to security tools like SIEM systems or log aggregators.
  • Traffic visibility: Many WAFs include dashboards that show threat trends, blocked IPs, and attack vectors.
  • Compliance enforcement: A WAF helps meet compliance requirements like PCI DSS Requirement 6.6, which mandates web application protection.

This makes WAFs useful not just for security teams, but also for developers and compliance officers.

WAF FAQs

A WAF filters incoming web traffic to block malicious activity before it reaches your application. It looks at requests, headers, cookies, and input data to detect attacks like SQL injection and cross-site scripting (XSS).

A traditional firewall blocks or allows traffic based on IPs, ports, and protocols. A WAF inspects the content of web requests and responses to block application-specific threats.

Think of it this way: a firewall guards your door; a WAF checks what people are trying to do once they’re inside.

The three main types of WAF are:

  • Cloud-based: Managed by a provider, easy to set up, scalable
  • Appliance-based: Hardware or virtual devices you manage yourself
  • Software-based: Installed on your own server, including host-based WAFs

If your site accepts input from users—whether that’s logins, search boxes, or contact forms—a WAF is essential. It helps block everyday attacks that could otherwise lead to data loss, downtime, or reputational damage.

Yes—Liquid Web offers Web Application Firewall (WAF) protection on fully managed VPS, cloud dedicated, and bare metal servers. The WAF is typically powered by ModSecurity, a host-based firewall that inspects incoming HTTP/S traffic and blocks common threats like SQL injection and cross-site scripting. 

Our WAFs are preconfigured with security rules and can be customized further for specific application needs. WAF protection is available for servers running Apache or NGINX and is managed by Liquid Web’s support team as part of their comprehensive security stack.

Next steps for understanding WAFs

Web application firewalls are not just for enterprise organizations—; they’re now a critical line of defense for any website or application that interacts with users. Whether you choose a cloud-based solution or a host-based firewall on your server, adding a WAF is a smart way to protect your site.

The next step is to choose a secure hosting solution that fits your needs, and that’s where Liquid Web comes in. We offer the industry’s fastest and most secure VPS and dedicated servers—for Windows or Linux, unmanaged or fully managed.

Click below to explore options or start a chat with one of our hosting experts now.

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Aaron Tevlowitz is a Partner Team Manager at Liquid Web, where he helps build and maintain strong partner relationships. Aaron has been helping business leaders design hosting solutions and drive growth for their companies since 2022. Aaron enjoys spending time with his family, staying active, and all things sports related. 

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