• Ramotion /
  • Blog /
  • Web Application Firewall: Definition, Importance, Types

Web Application Firewall: Definition, Importance, Types

What is a web application firewall? Explore the functioning and importance of WAF. Learn more about its types and role in improving web application security.

Written by RamotionOct 10, 202311 min read

Last updated: Oct 10, 2023


Increasing internet accessibility has made remote availability of services a necessity for modern businesses. Users expect smooth connectivity to required products and services from their homes.

Hence, enterprises must explore new avenues to ensure a high-quality customer experience. It has led to the availability of multiple web services in the modern digital space, like web applications.

The aim is to enhance the connection quality between businesses and customers. Web application developers must work on different aspects of the entire app to create an improved user experience. Moreover, the diverse use of web applications has made them a standard tool in various business sectors.

While the dynamic and customizable use of web applications has contributed to their growing popularity, it has also raised possible security concerns. Web application attacks are a threat to businesses and users. Hence, developers find appropriate solutions that provide a secure connection to web applications. A web application firewall is one tool to ensure a secure web connection.

In this article, we will explore the functions and importance of a web application firewall. You will also learn about its different types and deployment methods to enhance the security measures for your web applications.

Read along to understand the impact of web application firewalls on improving the security of modern businesses in the digital era.

Defining Web Application Firewall

A web application firewall is a protective firewall that monitors and filters HTTP traffic between a web application and the Internet. A WAF ensures application security from critical web application attacks.

It offers security solutions that detect any malicious activity within the HTTP traffic. It secures web applications from SQL injection attacks, DDOS attacks, cross-site scripting, and more.

Web application firewalls are an advanced version of a typical computer firewall developed in the 1980s. The initial firewalls looked at individual data packets to check for their source and followed the rules to pass through. Subsequent iterations analyzed the state of connections of the data packets and later moved into the application layer.

A Web Application Firewall Provides Secure Filtered HTTP Traffic (The Cloudflare Blog)

On the other hand, a web application firewall inspects the HTTP traffic going to a particular web application instead of traffic between servers.

The WAF will protect the application from external attacks without affecting its performance. However, it keeps reports and logs of all actions that enable developers to keep track of any attacks occurring at the backend.

Moreover, the WAFs have also gone through a progressive journey over the years based on the varying types of attacks on web servers and applications.

While blocklisting helped in the earliest stages against attacks on local server resources, WAF 2.0 became essential to deal with common attacks on web applications. It offered sensor monitoring, traffic optimization, and supervised ML processes.

However, the attacks on the applications advanced when the targets shifted to business logic instead of the applications. It led to the creation of WAF 3.0, which offered advanced hybrid protection and adapted to business logic.

Digital architecture has become more complex today, putting business logic, users, and intersystem communication at risk. The latest WAF 360º offers the most layered protection from web application attacks.

How does a WAF Work?

Web application firewalls work as a shield between a web application and the Internet. They protect web applications by monitoring, filtering, and blocking any malicious traffic directed toward the web application. A WAF operates through a set of rules called policies that ensure application security by protecting web apps against vulnerabilities.

While a proxy server acts as a mediating body to protect a client's identity, a WAF works in reverse - also called reverse proxy - by becoming an intermediary to protect web servers from any malicious clients. It primarily analyzes the GET and POST requests of an HTTP conversation. A GET request retrieves data from the server, while a POST request sends data to the server.

The following are three approaches used by WAFs to analyze HTTP requests:

  • Whitelisting: WAFs deny access to all requests by default and only process ones that are known to be trusted
  • Blacklisting: WAFs restrict access to traffic that looks malicious based on preset and managed rules
  • Hybrid: it provides web apps with a mix of whitelisting and blacklisting features as a security policy

WAFs come as software, an appliance, or delivered as a service. They allow users to set up custom rules for their application’s software per their needs. The request body must ensure that it matches the rules to gain access to the web application.

The Importance of a WAF

Mobile applications are a common and powerful tool for modern-day businesses due to the increased interaction of customers over the Internet.

As a result, application layer attacks become an attractive way for hackers to access vital data and information. It makes WAF a necessity for protecting web applications from malicious attacks.

WAFs Redefine Modern-Day Web Application Security (UK Tech News)

Some of the leading benefits of deploying web application firewalls in today’s digital networks are:

Protection from Threats

WAFs handle multiple attack vectors in the web traffic to protect web apps from potentially malicious requests. It monitors the traffic closely to identify vulnerabilities and allow or deny access accordingly.

Improved Security Solutions

WAFs block several types of threats online, including spyware, viruses, phishing, and other cyber-security attacks. It ensures the security of critical user data. It enables improved security rules that make WAFs a vital component of applications handling sensitive data, like online banking apps.

Protection from Bad Bots

Rapid development in AI has led to bots taking up a large share of internet traffic. Web servers rely on WAFs to identify and protect against bad bots in the traffic. It uses data-based behavior analysis, user-agent knowledge, and real-time intelligence to block attacks from bad bots.

Customized Configuration

The many versions of WAF ensure it is a dynamic and versatile solution. It enables the users to alter security rules as per their needs. The custom rules allow effective handling of business logic flaws and zero-day attacks. Thus, WAFs can be custom-configured easily.

Enhanced Website Performance

The improved security and coupling with the content delivery network (CDN) enhances website performance with WAFs. Web servers are only sometimes involved since the data is requested from the closest data center. It improves the speed of web applications.

Since data is a crucial asset for every business in the digital world, cyberattacks have also become increasingly complex. As a result, every online business, ranging from banking and E-commerce to healthcare, prefers to deploy web application firewalls to avoid data theft and fraud attacks.

Types of Web Application Firewalls

Hackers work to seek broken access control in web applications. Since it puts essential information at risk, businesses opt for WAFs to ensure the improved security of their networks. The web application firewalls are categorized based on the connectivity of a WAF with the rest of the network.

Let’s look at the three major types of web application firewalls and their connection to any digital network.

1. Host-based WAF

Host-based WAF's major benefit is its complete integration into the application’s code. It lowers the cost as it removes any hardware requirements from the process. Moreover, it offers better customization of WAF policies due to better integration with the application software.

However, it demands the installation of specific libraries on the application server. It makes the deployment of WAFs a more complex and lengthy process that relies on server plugin resources to work efficiently.

2. Network-based WAF

A network-based WAF is also known as hardware-based or appliance-based. It is deployed locally on-premises using a particular appliance. It reduces latency and enables large-scale scalability of WAFs. However, network-based WAFs are the most expensive option and need maintenance and storage of physical equipment.

An alternative is available using a virtual appliance that reduces the initial investment, but the maintenance expenses remain unaffected.

3. Cloud-based WAF

Cloud Native WAFs are the Simplest Type of WAF (XaaS Journal)

It is the simplest type of WAF that offers a low-cost connection of a WAF with a web application. Cloud-based third-party cloud service providers mainly manage cloud-based WAF or cloud-native WAF.

They provide a turnkey installation that changes the DNS or proxy configuration to redirect traffic through the WAF. It has a minimal upfront cost and ensures the latest threat intelligence that minimizes broken access control.

However, cloud-based WAFs require more organizational control as a third party handles the security and traffic management.

Companies must closely examine their WAF requirements before choosing a type to deploy into their digital network. All web application firewalls ensure better data security and improved network performance, with slight differences in their integration into the system. It would help you balance your requirements and financial constraints when choosing a WAF category.

WAF Deployment Methods

Web application security is crucial for organizations to protect their information from external attacks.

While a cloud-native WAF is the easiest to implement and network-based is the most complex type of WAF, each category can be deployed differently. Web application firewalls have three main deployment methods for any WAF type.

Web Application Firewall is Deployed in Three Major Ways

Let’s take a look at the available deployment methods of WAFs.

Reverse Proxy

It enables a web application firewall to act as a proxy to the application server. The traffic goes directly to the WAF instead of a web server.

Transparent Reverse Proxy

As the name suggests, the reverse proxy deployment of WAF is completed in a transparent mode. The web application firewall then sends filtered traffic to the web application separately.

As a result, the address of the application server remains hidden due to IP masking. While the transparent deployment methods ensure greater data security, latency and downgraded performance are its significant issues.

Transparent Bridge

It ensures complete transparency of a WAF between the web server and the user device. It allows the traffic to go directly toward the web application.

It would help if you kept the following considerations in mind when choosing a suitable deployment method:

  • Performance - the WAF architecture must be capable of handling high traffic without latency or additional delays and work well with CDNs
  • Compatibility - the deployment method must be compatible with the type of WAF used within the network and allow easy customization
  • Regulatory requirements - the web application firewall deployment must adhere to the organization-specific regulations, including data protection regulations and regional privacy laws.

It would help if you thoroughly explored your options within the specific context to make an educated choice of a web application firewall for your company. The ultimate goal of using a WAF should always remain central in your decision to protect your web applications.

Stepping Up Web Application Security With WAFs

Guarding the network traffic is necessary to ensure the protection of data and information. Different types of firewalls deal with varying kinds of protection.

While traditional firewalls protect against unauthorized access, web application firewalls monitor and filter data packets at the application layer. The variation in protection methods leads to multiple security models for companies.

WAF Security Models Offer Dynamic Data Protection (Security Intelligence)

Let’s look at different security models to enhance the protection of digital networks with WAFs.

Positive Security Model - Allowlist

Based on a positive security model, it allows traffic only from an approved list - called an allowlist. The positive model enables the web application firewall to allow access to selective inputs instead of filtering out malicious ones.

Thus, the web application is used only for safe traffic and is secure from new attacks, but is limited by its allowlist to handle traffic on a wide scale.

Negative Security Model - Blocklist

Its functionality is the opposite of a positive security model. Its premise is to deny access to a known list of attacks, called the blocklist. It poses a significant challenge where developers can never be sure to have addressed all possible attacks, leaving the web application vulnerable to new attacks.

However, the model is more accessible, especially for organizations that continuously change their network settings.

Hybrid Security Model

While traditional WAFs functioned on either a positive or negative security model, modern firewalls take an advanced approach to a hybrid security model.

It integrates different elements of both the allowlist and blocklist to ensure a more dynamic application security model.

An Additional Feature: Signature-Based Detection

It is an added feature included in modern-day WAFs. It searches for known and specific malicious patterns in the traffic and blocks them.

Each security model ensures rule matches based on different ideas of allowing or denying access. Companies can customize WAF policies to follow a security model most suitable for their digital network.

While the hybrid security model offers the most versatile application security, an allowlist is more efficient in networks with restricted access to a specific group of individuals, and a blocklist works well in a system where cyberattack categories can be easily determined.


Web application firewalls play a central role in improving the security and performance of web applications. They protect web apps from potential threats online by enabling users to put security rules in place.

The growing complexity of digital threats and attacks has led to the increasing use of WAFs in various industries. Web servers become a secure place for web applications with customizable WAF policies.

Its types include host-based, cloud-native, and network-based web application firewalls. They protect the application layer from potential attack through different deployment methods based on WAF’s position with the incoming traffic.

Moreover, WAFs are compatible with multiple security models, resulting in a more efficient process of protecting applications. Organizations must closely analyze their requirements to choose the most suitable WAF option.