Exploring the Difference Between a WAF and a Firewall

Unlike network firewalls, WAFs protect web applications from attacks that exploit unique vulnerabilities. Think of a WAF as a security guard at the entrance of your building – it allows only those recognized as safe to enter and blocks all others.

It can use an allowlist or blocklist model based on attack signatures and security rules. However, new vulnerabilities always emerge, and regular monitoring and rule updates are essential to mitigate threats.


The difference between WAF and a firewall is often misunderstood, especially by those who need help understanding how each type of system works. Firewalls are generally hardware or software designed to protect a network from unauthorized activity and attacks. Many personal computers have a built-in firewall ready to use, and most large companies will employ some form of firewall technology in their data centers.

Firewalls work at the Network and Transport layer of the OSI model (which could be regarded as a bible map of how networks function). They are generally concerned with network packet transfer between hosts and transforming that data to a destination host. Conversely, WAFs are primarily concerned with the application layer close to the user and the software or interface they will use to interact with that network.

As a result, WAFs are designed to offer protection against common web application threats such as SQL injection, cross-site scripting (XSS), and DDOS attacks. WAFs can be implemented as either software or hardware appliances. They can operate either in a passive mode, where it simply observe traffic without taking any action, or in an active inspection mode, scanning continuously for threats.

WAFs can also be deployed hybrid, with other security technologies such as an IPS or classic firewall. This is particularly beneficial for businesses looking to meet the Payment Card Industry Data Security Standard (PCI DSS), which requires all CHD enterprises to have a firewall. Firewalls differ from WAFs in that they have access control features that allow them to restrict or deny incoming requests, whereas a WAF does not provide this level of granularity. 


A WAF sits between external users and web applications, analyzing HTTP communication to detect and block attacks. This protects web apps from zero-day threats and other application layer attacks that bypass network firewall protections.

Most WAFs operate under a negative security model, where rules block connections that match known attack signatures. This is a good solution for protecting against well-known vulnerabilities and attacks. More advanced solutions can also use a positive security model, where rules allow connections that meet defined criteria.

Firewalls operate at the network layer, OSI layer 3, while WAFs operate at the application layer, OSI layer 7. As a result, they have different rules and use different algorithms to identify malware. WAFs run anomaly detection and heuristic algorithms, while firewalls use packet filtering algorithms to determine whether a connection is legitimate.

WAFs are used by organizations to safeguard against a variety of attack patterns, including database injections, XSS, and command injection, which execute malicious code in the browser to gain unauthorized access or manipulate data. A WAF is essential, especially in e-commerce environments where sensitive customer data is transmitted via the Internet. 

Intrusion Prevention Systems (IPS)

In addition to detecting and blocking threats, WAFs protect businesses from data leaks and provide tools for compliance with security standards like the Payment Card Industry Data Security Standard (PCI DSS). To fully protect web applications, however, using a WAF in conjunction with other security tools is important.

Firewalls operate at the network layer and use information like IP addresses and ports to decide whether or not network traffic should pass through a given port or address. As the Internet evolved, it became clear that there was a need to provide additional protection at the application layer. WAFs analyze HTTP interactions and reduce or eliminate malicious activity and unauthorized communication before it reaches a web application server for processing.

Unlike firewalls that operate in real-time and can take swift action, IPS examines ongoing network traffic to detect and prevent threats before they occur. An IPS solution is placed within flowing network traffic to inspect individual packets of data in real-time, meaning that they can quickly and accurately respond to emerging attacks.

An IPS may use multiple detection methods to recognize threats, including signature-based, behavioral analytics, and anomaly detection. Signature-based detection compares current network activity with known patterns of previously spotted cyberattacks, which can easily deflect attacks that have been detected before. On the other hand, behavioral analytics and anomaly detection look for suspicious behavior that hasn’t been spotted before to identify and intercept emerging threats.

Some IPS solutions will automatically respond to a threat by ending a user session, blocking a specific IP address, or sending a dangerous packet to a honeypot, where it can be scrubbed of its malicious contents. Alternatively, an IPS may prompt other security devices to act by updating a firewall rule to block a specific threat or changing router settings to cut off access to a particular target.

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