A WAF (Web Application Firewall) helps protect web applications by filtering and monitoring HTTP traffic between a web application and the Internet. It typically protects web applications from attacks such as cross-site forgery, cross-site-scripting (XSS), file inclusion, and SQL injection, among others. A WAF is a protocol layer 7 defense (in the OSI model), and is not designed to defend against all types of attacks. This method of attack mitigation is usually part of a suite of tools which together create a holistic defense against a range of attack vectors.

In recent years, web application security has become increasingly important, especially after web application attacks ranked as the most common reason for breaches, as reported in the Verizon Data Breach Investigations Report. WAFs have become a critical component of web application security, and guard against web application vulnerabilities while providing the ability to customize the security rules for each application. As WAF is inline with traffic, some functions are conveniently implemented by a load balancer.

According to the PCI Security Standards Council, WAFs function as “a security policy enforcement point positioned between a web application and the client endpoint. This functionality can be implemented in software or hardware, running in an appliance device, or in a typical server running a common operating system. It may be a stand-alone device or integrated into other network components.”

By deploying a WAF firewall in front of a web application, a shield is placed between the web application and the Internet. While a proxy server protects a client machine’s identity by using an intermediary, a web firewall is a type of reverse-proxy, protecting the server from exposure by having clients pass through the WAF before reaching the server.

A WAF operates through a set of rules often called policies. These policies aim to protect against vulnerabilities in the application by filtering out malicious traffic. The value of a WAF management comes in part from the speed and ease with which policy modification can be implemented, allowing for faster response to varying attack vectors; during a DDoS attack, rate limiting can be quickly implemented by modifying WAF policies.

WAF solutions can be deployed in several ways—it all depends on where your applications are deployed, the services needed, how you want to manage it, and the level of architectural flexibility and performance you require. Do you want to manage it yourself, or do you want to outsource that management? Is it a better model to have a cloud WAF service, option or do you want your WAF to sit on-premises?

A WAF products can be implemented one of three different ways:

• A network-based WAF is generally hardware-based. Since they are installed locally they minimize latency, but network-based WAFs are the most expensive option and also require the storage and maintenance of physical equipment.
• A host-based WAF may be fully integrated into an application’s software. This solution is less expensive than a network-based WAF and offers more customizability. The downside of a host-based WAF is the consumption of local server resources, implementation complexity, and maintenance costs. These components typically require engineering time, and may be costly.
• Cloud-based WAFs offer an affordable option that is very easy to implement; they usually offer a turnkey installation that is as simple as a change in DNS to redirect traffic. Cloud-based WAFs also have a minimal upfront cost, as users pay monthly or annually for security as a service. Cloud-based WAFs can also offer a solution that is consistently updated to protect against the newest threats without any additional work or cost on the user’s end. The drawback of a cloud-based WAF is that users hand over the responsibility to a third-party, therefore some features of the WAF may be a black box to them.