Web Application Firewalls (commonly referred to as WAF) are mainly designed to protect web applications.
But what exact roles can they play in a web architecture?
Depending on how they are integrated in your web platform, their impact and ability to improve your security will differ.

Using a WAF as an attack mitigation solution

A WAF can be used to analyse inbound and outbound traffic in order to block malicious or dangerous items.

In this configuration, the threat detection engine of the firewall detects suspicious inbound traffic and decides to block the request. This means that the request will not reach the web server, and a generic response will be returned to the client.
To decide whether a request is innocuous or malicious, the WAF can use a positive or a negative security model:
The negative security model assumes that all transactions are innocuous, by default. It will look for threat cues and if judged dangerous, block the transaction.
The positive security model, on the other hand, assumes that all transactions can be dangerous and only allows those that are recognized as safe.

As cybersecurity issues increase, Web application filters and Web Application Firewalls are becoming more popular. These tools can be an excellent first step towards securing your applications. How do they work? What is the difference between them? Please read the following lines for an introduction of this topic.

Filters or WAF: Who’s who?

The first kind of defense is called “Filtering”. Whether implemented as part of a development framework or implemented by the developer himself, filtering is in the end part of the application.
Of course the efficiency of this protection will depend on the awareness of the developers on security and also on their experience in developing secure applications.

The second type of defense is called WAF (Web Application Firewall). This type of product is not to be confused with “usual firewalls”, in the sense that web application firewalls analyse the web traffic and don’t stop at filtering traffic based on a particular port number, address or protocol.
Web application firewalls can be implemented on the web server itself, or in front of the web server (between the end-user and the web server).

We assume here that your hosting environment is already secure, whether managed by yourself or by a hosting provider.
Let’s focus on the applications. What steps can you take to improve the security of a web application? How to reduce the attack surface and remove easily detectable risks? This article does not pretend to be the manual of the perfect web application defender, but recalls basic principles and presents a list of items to be considered and applied on a regular basis.