Web Application Firewall – Your Server’s Watchdog

The internet is filled with different types of traffic. Some are organic, but most of them are bot driven. This bot traffic could either be helpful, like search engine bots, or highly harmful to your websites and servers. Many tools exist to keep your website free of these harmful agents, and a Web Application Firewall (WAF) is one such application.

What Is a Web Application Firewall (WAF)?

A WAF, called a WAF in short, is a program that helps monitor and regulates the content that your server can access through the internet. The traffic is screened for any possible malware and other malicious content such as Cross-Site Forgery, Distributed Denial of Service (DDoS) attack, Structured Query Language (SQL) Injection, Cross-Site Scripting, security breaches, spyware content, among others. This software acts as one of the necessary barriers that ensures only safe data reaches your server among heavy unregulated traffic. 

Special Features of a WAF

A WAF can be taken as analogous to a proxy server, just that it acts in the exact opposite direction. While Proxy servers protect your identity from various websites on the internet, a WAF guards your server against the hoard of incoming traffic. Users are screened by this program and verified before being given access to your data. 

This sentinel to your server is a protocol layer 7 defense based on the OSI model. Although a WAF is very effective, it does not protect against all kinds of threats. It needs to work in conjunction with other programs to be maximally effective. 

How Does a WAF Work?

Like all other programs, a WAF works based on preset rules. The rules here are called policies. These policies undergo modifications based on the kind of threat that is posed to the server. This, in turn, determines the efficacy of the WAF. The speed with which it detects a threat and modifies to fix it is a true testament to this. A faster response indicates a better WAF.

How Does It Differ From Other Server Protection Services?

A WAF focuses solely on internet-based attacks. This is precisely at the application layer, and other programs such as packet filtering, etc, cannot do this. It is a proxy firewall that functions on the protocol 7 layer. This makes it a necessary and valuable component to defend your server. 

What Are the Different Varieties of a WAF?

There are 3 common types of WAFs – 

1. Host-based WAF: 

This type of WAF is completely integrated into the host server. It is relatively inexpensive as compared to the other types and provides more scope to modify and tailor it to your server. This, however, adds a few drawbacks, which include an increase in the complexity of the program. This is compounded with a need for regular maintenance and a need for a lot of locally placed resources. The latter adds to the complexity and cost, making it affordable only to selective hosts. 

2. Network-based WAF: 

These WAFs provide a minimal delay in screening hosts because the firewall is based locally on a hardware device. Equipment, however, is more expensive than a storage platform based on the internet, and it requires both physical and software maintenance. This makes the network-based variety the most expensive form of a WAF.

3. Cloud-based WAF:

These WAFs are easy to operate, install (they have a turnkey installation), and maintain. They are the most cost-effective alternative and require the host to pay a monthly fee and a service fee whenever required. The WAF provider offers many updates to the latest version without any cost, and this saves the client the task of constantly updating. This lucrative alternative comes with its own drawbacks. The authority to provide and handle it is handed to a third-party vendor. This gives the vendor the authority to shut out any user they find as a threat, and updates (which may be buggy or unnecessary) may be forced upon you. 

Different Models of WAFs

A WAF may work based on a Positive Security Model or a Negative Security Model.

1. Positive Security Model: 

This model is also called the Allowlist model. This works by allowing the traffic that is approved beforehand by the server host. This WAF acts as the gate to a ticketed event that gives access only to the ticket holders. This allows only a select crowd to access the server. It has its own drawbacks too. Once the list is set, rarely make any allowlists permit additions. Accidental additions cannot be removed too at the last minute. This, therefore, requires careful discretion on behalf of the host. 

2. Negative Security Model:

This model is also known as the blocklist model. This WAF works by denying entry to any client it deems as a threat to the server. As an example, it can be thought of as an immigration officer screening who is deemed fit to enter the country. This model comes with the drawback that once a malicious user has entered, the damage may have been done by the time the firewall detects and denies access into the server. 

Due to their contrasting features, providers generally offer WAFs that have both the models incorporated. 


Protecting your web-based content in today’s era is of utmost importance. I hope that through this article, I have provided some insight into the workings of a WAF. This, when used with other security measures, can secure your server and offer you a safe traffic handling outpost.

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