A Web Application Firewall (WAF) is a security tool that monitors, filters, and blocks HTTP traffic to and from a website or web application. WAFs can be set up on a network, a host server, or in the cloud. They are deployed through a reverse proxy, positioned in front of one or more websites or applications.  

Whether running as a network appliance, server plugin, or cloud service, the WAF examines each data packet and uses rules to analyze web server traffic, filtering out potentially harmful data that could lead to web exploits. 

WAFs are commonly used by businesses to protect their web systems from a variety of threats, including zero-day exploits, malware, impersonation, and other known and unknown vulnerabilities. Hence it is essential to  

Here are more details to help you understand what a web application firewall is. 

How Does a Web Application Firewall Work? 

To understand how a Web application works, first understand that WAF can be implemented as software, a physical device, or a cloud service. It analyses HTTP requests and applies rules to determine which parts of the conversation are safe and which can be a threat. 

The focus of a WAF is on GET and POST requests. GET requests are used to fetch data from a web server, while POST requests send data to a web server. 

A WAF can analyze and filter HTTP requests using three different approaches: 

  • Whitelisting: This approach blocks all requests by default and only allows those from known and trusted sources. While it is efficient and less resource-intensive, it can sometimes block traffic to the website. 
  • Blacklisting: This method blocks requests that match known malicious patterns or signatures. It is more suitable for public websites that receive traffic from various sources. However, more resources and detailed information are required to identify harmful packets accurately. 
  • Hybrid Security: This model combines both whitelisting and blacklisting to provide a balanced approach. 

Whatever the method, a WAF inspects HTTP traffic to reduce or eliminate malicious activities before reaching the server. The policies need regular updates to stay effective against new threats. Modern WAFs with machine learning capabilities can even update automatically to adapt to emerging threats and vulnerabilities. 

Why is a WAF Important? 

WAF is especially crucial, for businesses that offer products and services over the internet, such as banks, social media platforms, and mobile app developers. It helps prevent data breaches by protecting sensitive information, like credit card details and customer records, stored in back-end databases that web applications access. Attackers often target these applications to steal data. 

For example, banks use WAFs to comply with the Payment Card Industry Data Security Standard, a set of rules designed to protect cardholder data. One requirement is to install a firewall, which applies to any company handling card data. With the rise of mobile apps and the Internet of Things, more transactions happen through web applications, making WAFs essential for modern business security. 

In an enterprise security model, a WAF works best alongside other security tools, like Intrusion Prevention Systems (IPS), Intrusion Detection Systems (IDS), and traditional or next-generation firewalls (NGFW). This combination provides a stronger defence against cyber threats. 

Features and Benefits of WAFs 

There are several notable features of WAFs besides protecting against common web attacks. These features can help improve performance and maintain compliance, making them a vital tool for protecting web applications. 

  1. Web Application Attacks: WAFs can detect and prevent common web attacks like SQL injection, cross-site scripting, and buffer overflows by blocking or limiting suspicious traffic. 
  2. Detailed Tracking: For investigating potential security issues, WAFs keep detailed logs and offer monitoring capabilities. For example, Amazon Web Services (AWS) provides monitoring options like AWS CloudWatch Alarms, AWS CloudTrail logs, and AWS WAF web access control list traffic logging. 
  3. Traffic Pattern Analysis: With the help of AI algorithms, WAFs can analyze traffic patterns. They establish behavioural baselines to detect unusual activities that might indicate an attack. 
  4. Identifying Malicious Requests: If there are any malicious requests, WAFs profile applications can examine their structure, common queries, URLs, values, and allowed data types to identify and block harmful requests. 
  5. Enhanced Performance: WAFs configured at the network edge can offer CDNs to cache websites, reducing load times. They deploy CDNs across multiple international locations to serve users from the nearest point, reducing latency. 
  6. Tailored Security Rules: Organizations can apply specific security rules to application traffic, customizing the WAF’s behaviour to meet their needs and avoid blocking legitimate traffic. 
  7. Handling High Traffic: Most WAFs can scale to manage high-traffic websites and applications. They are also flexible, with deployment options ranging from on-premises to cloud-based environments. 
  8. Extra Security Layer: Establishing WAFs provides an additional layer of protection against web attacks, helping organizations comply with regulations and protect sensitive user data. 
  9. Protection Without Code Changes: Without access to the source code WAF can protect applications. While host-based WAFs integrate into application code, cloud-based WAFs can defend applications externally. Cloud WAFs are easy to deploy and manage, offering quick virtual patching to adapt to new threats. 

Types of Web Application Firewalls 

Here are the three most common types of Web Application Firewalls  

Network-Based WAFs 

Network-based Web Application Firewalls are primarily hardware devices installed on-premises as close to the application as possible. This proximity offers several advantages, including reduced latency because the firewall is local to the network.  

Additionally, these WAFs allow for the easy replication of rules and settings across multiple devices, making them suitable for large-scale deployments. However, network-based WAFs are generally expensive, not only due to the high initial purchase cost but also because of the ongoing maintenance expenses. 

Host-Based WAFs 

Host-based Web Application Firewalls are integrated directly into the application’s code. This approach offers a high degree of customization and is typically more cost-effective compared to network-based solutions.  

However, managing host-based WAFs can be complex. They rely on the local server’s resources and require specific application libraries, which can consume significant system resources. Additionally, managing these WAFs often requires a team of developers and system analysts to ensure proper integration and maintenance. 

Cloud-Hosted WAFs 

Cloud-hosted Web Application Firewalls are a popular choice due to their affordability and ease of deployment and management. These WAFs are available on a subscription basis and typically require only a simple DNS or proxy change to be activated.  

Managed by third-party providers, cloud-hosted WAFs benefit from the latest threat intelligence, ensuring up-to-date protection. While relying on a third party for security can present challenges, such as trust and control issues, this model offers consistent protection across various hosting locations, making it an attractive option for many organizations. 

A Web Application Firewall (WAF) is essential for identifying and preventing some of the most critical web application security threats that traditional network firewalls and other security systems may overlook. This helps identify and block potential threats more effectively, thereby making your business safe from any malicious intent or cyber threats. 

This makes WAFs particularly beneficial for banks and companies providing internet-based services, such as e-commerce, online banking, and other online customer or partner interactions.