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What is a WAF? | Web Application Firewall

What is a WAF? | Web Application Firewall

One of the issues and problems many businesses are dealing with these days are hacker and cyber attacks involving information systems and websites. Firms and companies use different and advanced security systems to deal with such attacks.

WAF, or Web Application Firewall, is a security system that protects web applications from Internet attacks. By analyzing web traffic and identifying patterns episodes such as SQL Injection and Cross-Site Scripting attacks, WAF prevents these attacks from entering web applications.

One of these security systems is WAF or Web Application Firewall. A WAF is a security system installed on websites and web applications that automatically protects against cyber attacks such as XSS and SQL Injection attacks.

For this, by default, p, Europa, e, check checks all incoming and outgoing traffic using its own rules and algorithms and automatically blocks it if any cyber attack is detected.

One of the advantages of using WAF is that it allows companies and organizations to protect against various cyber attacks without changing their application code and prevent hackers from accessing thinformativeion.

To better understand the concept of WAF, we will tell you a story. (Our story is a little rough, people with heart disease, don’t read)!

Imagine a war front where the soldiers are stationed. There are trenches and dangerous attacks from the enemy, like shooting. These soldiers are responsible for guarding and protecting. The strategy that these soldiers should use is to choose one of them as a guard to respond to these attacks. What this guard has to do is detect attackers and protect the wall from attacks by taking actions such as performing some operations or responding to threats (the same thing that WAF does against hacker attacks). ).

So far, you are familiar with the concept of WAF. Still, the story is a bit complicated, and that’s why we will answer the question of what is WAF system in the simplest possible way in this comprehensive article. So don’t miss this exciting article and stay with us.

But first of all, we should point out that if security is your main concern, it is better to know that in virtual servers, WAF can be installed as an additional layer of security on top of the virtual web server to protect the web applications inside it. So, buying a virtual server can multiply your security.

Table of Contents

  • Why do we need WAF?
  • How does WAF work?
  • Types of WAF models
  • Difference between WAF and Firewall
  • What is the difference between blocklist and allowlist WAFs?
  • Network-based, hosted, and cloud-based WAFs
  • Why is web firewall security of applications critical?
  • Types of web application firewalls
  • What features and capabilities does WAF have?


Why do we need WAF?

Many organizations face application-level security risks due to agile development methods, migration to the cloud, increased use of web software or SaaS applications, and remote workforces. A WAF allows organizations to counter attacks targeting web applications and APIs.

Although WAFs do not protect organizations against all digital threats, they can be applied against threats targeted at the application level, including OWASP’s top application vulnerabilities. These vulnerabilities include:

  1. Cross-site scripting (XSS) attack: In this type of attack, the attacker places malicious code on a valid website. This code is then executed as an infected script in the user’s web browser, allowing the attacker to steal sensitive information or impersonate the user.
  2. Application-Layer DDoS Attacks: In this type of attack, the attacker tries to disrupt the service of a site by creating a high volume of malicious traffic so that it does not respond to regular user requests. Examples of these types of attacks include HTTP/S flushes, SSL attacks, and brute force attacks.
  3. SQL injection attack: In this attack, the attacker injects malicious SQL commands into a program by taking advantage of a known vulnerability. This action allows the attacker to extract, change or delete information.
  4. Zero-day attacks occur when a hacker takes advantage of an unknown security vulnerability or software bug before a software developer releases a patch. This means that the hacker works against an unspecified security vulnerability and uses it to enter the system and gain access to sensitive information.


How does WAF work?

This text states that when a WAF (a type of security system) is installed before a web application, a protective shield is placed between the web application and the Internet, blocking all traffic between the web application and the end user(s). supervises A WAF protects web applications by filtering, monitoring, and barring any malicious HTTP/S traffic traveling to the web application. It also prevents unauthorized data from leaving the web application by complying with a series of policies that help determine the level of traffic security.

Just as a proxy server acts as an intermediary, maintaining a client’s identity, in a traditional installation, a WAF works oppositely, acting like a proxy, as a reverse proxy, acts as an intermediary, and the application server. It protects the web from a potentially malicious client.

Types of WAF models

When it comes to security, WAFs typically follow three approaches:

  • Allowlisting: uses machine learning algorithms and behavior modeling to define which traffic to allow and block the rest.
  • Blocklisting: Defines a list of traffic that the WAF should block and accept the rest based on updated signatures for known vulnerabilities.
  • Hybrid Approach: In this method, WAF uses a combination of positive and negative security models; that is, it defines a list of elements that can be allowed to pass and a list of features that should be blocked to determine the allowed traffic.

Difference between WAF and Firewall

The main difference between a firewall and a WAF is that a firewall usually only protects the network and transport layers (layers 3 and 4). However, the web application firewall provides layer seven protection.

What is the difference between blocklist and allowlist WAFs?

A WAF based on a blocklist (negative security model) protects against known attacks. A WAF blocklist can be considered a security guard with orders to deny entry to guests who do not conform to the dress code. In contrast, an allowlist-based WAF (positive security model) lets in only pre-approved traffic. It’s like security personnel at an exclusive party; he only lets in people on the list. Both blocklist and allowlist have advantages and disadvantages, which is why many WAFs implement a hybrid security model that includes both.

Network-based, hosted, and cloud-based WAFs

WAFs are divided into three types: network-based, host-based, and cloud-based.

The first type of WAF is network-based, which uses hardware and is usually installed locally on the system. This type of WAF reduces the delay in the design, but its cost is very high and requires physical equipment to maintain.

The second type of WAF host can be focused on the server (host-based) and network-based (network-based). The server-centric version is wholly embedded in the application software. This solution is cheaper than the network-based type and allows for more customization, but using local server resources brings implementation complexity and maintenance costs. These parts usually require engineering time and high prices.

The third one is cloud-based Waps. Cloud-based web firewalls are a good, inexpensive option that doesn’t require sophisticated technical knowledge. These firewalls are usually quick and easy to install, and by changing DNS, it’s easy to route website traffic through them.

The cost of these firewalls is low because users pay for security monthly or yearly. Also, these firewalls are constantly updated and protect against new threats without the need for additional cost or exceptional work from the user. However, the problem with these firewalls is that users transfer the responsibility for their website security to a third party. Therefore, some of the features of these firewalls remain unclear to them.

Why is web firewall security of applications critical?

Application web firewalls are essential for many organizations that offer their products or services online, such as mobile application developers, social media, and digital bankers. Web firewall programs can help you protect sensitive data such as customer information and payment cards and prevent intrusion into this information.

Organizations store much of their sensitive data in a backup database accessible through web applications. Companies use mobile applications and IoT devices to facilitate their business interactions, and many online transactions are performed at the application layer. Attackers often attack applications to gain access to this data.

If you are an organization that works with cardholder information, you need high security to protect your customers’ information from internet attacks. One way to protect customer data is to use a WAF. A WAF acts like a firewall and helps protect your web applications from various attacks, including SQL Injection and Cross-Site Scripting attacks. Using a WAF enables you to meet security requirements such as PCI DSS.

But it is recommended to use other security measures such as IDS, IPS, and traditional firewalls to protect customer information. These security measures can be combined with WAF to achieve a multi-layered defensive security model that helps you protect your customers’ data and prevent cyber attacks from entering your system.

Types of web application firewalls

There are three main ways to implement a web application firewall:

Network-based firewall

This type of firewall is more hardware-based and is installed locally to reduce latency. However, this type of firewall is the most expensive and requires storage and maintenance of physical equipment.

Host-based WAF

It is fully integrated into the software of a program or application. This option is cheaper and more customizable than network-based WAFs, but it consumes many local server resources, is complex to implement, and is expensive to maintain. Usually, to run a host-based WAF, the machine used must be able to be enhanced and customized, which may be costly and time-consuming.

Cloud-based WAF

is a security solution that can be used without the need for initial capital by paying a monthly or annual security subscription. This way, you don’t need to pay extra for updates, and you don’t need to try to manage it. However, because a third party contains this security solution, you should ensure that the “Cloud-based WAF” has enough customization options to match your organization’s business rules.

What features and capabilities does WAF have?

WAF has various capabilities and features that we will name below and explain each one.

Attacking template databases

Attack patterns are likely to indicate malicious traffic, which can include a variety of requests, unusual server responses, and malicious IP addresses. In the past, WAFs usually relied on attack pattern databases, which were ineffective against new or unknown attacks.

Analyze traffic patterns based on artificial intelligence

With the help of artificial intelligence algorithms, you can use behavioral basics and analyze traffic patterns for different types of traffic. But what is the advantage of this work? You can detect anomalies associated with marker attacks and identify attacks that do not match known malicious patterns.

Application profile

Application profiling means analyzing the structure of an application, which includes typical requests, URLs, values, and allowed data types. This feature enables the WAF to detect and block suspicious requests.


Operators can define security rules applied to application traffic. This feature allows organizations to customize WAF behavior based on their needs and prevent legitimate traffic from being blocked. This means that organizations can avoid legal traffic restrictions by defining more appropriate security rules.

correlation engine

An “analyzer” system examines incoming traffic and plans it using signs and patterns known from previous attacks. They also decide whether traffic should be blocked using application analytics, AI analytics, and custom rules.

DDoS protection platforms

You can integrate a cloud-based platform, so attacking sites is not easy. In other words, protect against distributed denial of service (DDoS) attacks. If the WAF succeeds in detecting DDoS attacks, it will transfer site traffic to this cloud-based platform, and you can manage the high volume of attacks that occur.

Content Delivery Networks (CDN)

WAFs are placed at the network’s edge, so a WAF through a cloud host helps you provide a CDN, cache the website, and improve its loading time. The WAF distributes the CDN across multiple points that are spread globally, so users are served from the nearest PoP. This means that your website will load faster for users.

WAF technology

A WAF can be built into a server-side software or hardware platform as a plug-in or as a service to filter traffic. WAFs can protect web applications from malicious or compromised endpoints and act as a reverse proxy (as opposed to a proxy server that protects users from dangerous websites).

WAFs ensure security by intercepting and inspecting every HTTP request. Unauthorized traffic is tested using various methods such as device fingerprint recognition, analysis, and CAPTCHA challenge and blocked if not valid.

WAF can detect and block malicious attacks with the help of security rules. These rules typically include prominent security vulnerabilities in web applications maintained by an OWASP project.

But that’s not all; the organization can define its own custom rules and security policies to match the business logic of its application. But to set up and customize WAF requires particular expertise.


WAF security models

WAF can use two types of security models: positive and negative. In the positive security model, an allowlist allows only traffic to pass through. In the negative security model, a blocklist blocks only certain items. But this model cannot guarantee that all threats will be removed. The level of security depends on the number of restrictions that are enforced.

A WAF can use two types of security models: positive or negative security models or a combination of them.

In the positive security model, an allowlist filters traffic, and anything not on the list is blocked. This model can also block new or unknown attacks.

In the negative security model, a blocklist filters traffic, and only specific items on the list are blocked. This model is easy to implement but cannot guarantee that all threats will be removed. Also, maintaining a list of dangerous signals, which may be extended, is necessary to use this model. The level of security depends on the number of restrictions that are enforced.


In short, WAF or Web Application Firewall is a security system that protects web applications from attacks and security threats. WAF protects your web applications from SQL attacks, malicious code, communication vulnerabilities, and more.

You can use positive, negative, or mixed methods to set up a WAF, each with its characteristics, and you can use the appropriate form for each type of web application.

Also, WAFs can be added to virtual servers and other types of servers. To use WAF, you must configure it manually or using network management tools.

Finally, using a WAF can help you protect your web applications from security threats and give you more peace of mind.