How Does a WAF Work and What Attacks Does It Protect Against?

Recent findings from a Mozilla survey indicated that among the top one million websites, nearly all of them–more than 93 percent –failed to implement even the most basic cybersecurity measures to prevent common attacks. This is deeply concerning given the ever-evolving threat landscape. Application security is more critical than ever, and a WAF should be an essential part of every company’s toolbox to protect its websites against malicious actors.

What is a WAF?

A Web Application Firewall (WAF) is a filter for web applications that monitors HTTP traffic between that application and the Internet. Its purpose is to secure your web applications and suspect incoming traffic for suspicious activity, such as hacks and other threats.

How Does a WAF Work?

In simple terms, a WAF is a filter between your website application and the visitors to your site; it lets in the good visitors while keeping out the bad.

WAP for Servers

WAFs catch and block malicious web traffic before it reaches the server. They also have ways of testing whether suspicious traffic is malicious, such as by sending users a CAPTCHA challenge. Other WAFs can help you identify vulnerable areas in your web application by simulating attacks.

There are three types of security models for WAFs: whitelisting models, blacklisting models, and hybrid security models. A whitelisting model allows web traffic according to criteria that you specify while blocking all other visitors. This is a very tight way to secure a website, since it will block out all traffic that doesn’t match the specified criteria; while it will block out some traffic that isn’t malicious, it can be a good way to allow only a limited group of people, such as employees, into your network.

A blacklisting model essentially works the opposite way. Rather than specifying criteria for good traffic, it specifies criteria for bad traffic. It blocks clearly malicious web traffic while letting in everyone else. This is the standard type of WAF across the web.

The last type of WAF, the hybrid security model, works by blending the strategies of whitelisting and blacklisting models.

Each security model has its own advantages, and you should identify the best model for you based on the specific context of your web application and server.

 What Attacks Does It Help Prevent?

IPS, IDS, and standard firewalls help protect web applications to some degree, but they don’t prevent all attacks. For example, they do not protect against SQL injection or XSS attacks. A Web Application Firewall, on the other hand, can effectively defend against the following attacks:

Web Application Firewall

Cross-Site Scripting (XSS)

Cross-site scripting involves the injection of malicious data into websites. Such attacks happen when an untrusted source hacks into and injects its own code into a web application.

Cross-Site Request Forgery (CSRF)

CSRF forces the end-user to take actions on the attacker’s behalf. An attacker could trick both ordinary people and administrative users (for, example, by sending a link in an email) into executing actions such as transferring funds or changing their email address.

Structured Query Language (SQL) Injection

SQL injections involve hackers using an input box on a web form to gain access to the site’s database. In this way, the attacker is able to steal and alter the data in the database.

File Inclusion

File inclusion vulnerabilities occur when a hacker is able to upload files to the server or submit input into files. This may allow the hacker to gain access to sensitive data or inject malicious code into the web server.


WAFs work by filtering and monitoring your web traffic, and they protect against attacks such as XSS, CSRF, SQL injection, and file inclusion. They’re a more reliable and less time-consuming way to protect a website than either keeping up with hacking trends yourself or expecting your web host to take care of it for you. WAFs are a critical part of any company’s cybersecurity strategy, and a proactive way to ensure company and website data stays safe.

While most of the people around the world are busy in arguing about whether Android is better or iPhone, Jon is busy in exploring both of these platforms to find their pros & cons. Yes, he owns both and he loves to shares helpful tips, tricks, apps & hacks for Android & iOS by the means of our website.