What is a WAF?
A web application firewall (WAF) is a distinct security firewall solution used to monitor and sanitize web requests and their responses. It creates a protective shield between web apps and the internet, preventing many common attacks. By monitoring all requests sent to the web server and checking the responses, a WAF acts as a reverse proxy for the web server that attempts to detect possible attacks.
WAFs were initially created to deal with threats that traditional firewalls could not handle. These firewall-evading threats were dangerous because they took advantage of authorized security protocols, such as HTTP, to attack web applications.
Before the inception of WAFs, malicious actors could compromise systems and steal information directly over these trusted protocols. Therefore, the need arose for a more thorough security layer — especially as web applications became increasingly prevalent.
Cyber-attackers are constantly using new and inventive tactics to orchestrate attacks against web applications, servers, and APIs — all of which are critical for most businesses today.
Web applications are most commonly attacked by SQL injection, cross-site scripting (XSS), cross-site request forgery (CSRF), cookie poisoning, and DDoS (distributed denial-of-service) attacks. WAF protects against these attacks (among others) by filtering the HTTP traffic to and from the web application.
WAFs sit between users (clients) and web applications to monitor and analyze all HTTP communication between both parties to detect, filter, and block malicious data packets in traffic before they reach users or web applications. They protect your web application and server against threats like web shells, ransomware, malicious payloads, and phishing and keep unauthorized data from leaving the app.
However, despite the ability of WAFs to block specific security attacks, they’re not designed to offer complete protection against all types of threats. They’re intended to complement and cooperate with your security suites, such as traditional firewalls and intrusion prevention systems.
Why use a WAF?
Sensitive data is frequently exchanged at the application level in user accounts, transactions, and more. Typically, this data is stored in back-end databases accessible via web applications. Unfortunately, these back-end databases are frequent targets of attacks.
Apps are the gateway to valuable data, which is why they’re the most common target of breaches. As a result, you must have the proper security measures to safeguard customer data against these threats.
Typically, businesses have protected their data and users with traditional firewalls, which don’t offer the flexibility or transparency needed to safeguard against some modern security threats. Because WAFs are an application-level security mechanism, they help to protect both your application and their backend databases.
WAF protects web applications from various types of malicious attacks by constantly monitoring them for potential threats and blocking them if they indicate malicious activity. As such, implementing a WAF can prevent attacks that seek to compromise your systems and exfiltrate your data.
Fortunately, implementing a WAF is an easy and cost-effective way to improve the security of any application network. A WAF is essential to any thorough security strategy — and is critical for companies offering products and services online.
How Does a WAF Work?
WAFs are typically placed between users and web servers to analyze and compare network traffic with vulnerability databases. By residing in front of a web application, meaning outside of your network, a WAF can act like a shield between the web application and its users by monitoring all communication between users and the app. For example, when a user logs in to an application and sends their login and password, the WAF can verify that the authentication data contains no malicious code.
WAFs operate using a set of known rules called policies. The WAF inspects each packet and analyzes application data, filtering out suspicious or dangerous traffic based on these rules.
A policy can be customized to meet the specific needs of one or a group of applications. Many WAFs need you to update their policies regularly to address new security vulnerabilities manually. However, some WAFs have sophisticated machine learning features that enable them to update automatically.
There are three possible actions a WAF can take if malicious code is detected in application payloads, whether sent by users or received via compromised web apps:
- The WAF can filter requests containing malicious data and then discard them. Based on the configuration, the WAF may notify the client or silently discard the request.
- In the case of sanitization, potentially malicious content is automatically converted to harmless content using a process called escaping.
- WAFs may log all or selected severity levels of potentially malicious requests depending on their configuration. This data can then be analyzed separately to provide threat intelligence.
Furthermore, some WAFs enable you to set alerts that inform you of suspicious traffic patterns, so you’ll receive an email whenever an attack is suspected.
Types of WAFs
Hardware-based WAFs, sometimes referred to as network-based WAFs, act as gateways between devices and appliances inside and outside your network. Since hardware-based WAFs can replicate rules and settings across different machines, they’re ideal for enterprises.
In contrast to the other two types of WAFs, they’re installed locally as on-premises devices, which reduces latency. However, they’re the most expensive option to implement due to the costs associated with purchasing, storing, and maintaining physical equipment.
A host-based WAF, sometimes called a software-based WAF, can be integrated into an application’s software. Host-based WAFs run on servers and have the advantage of being less expensive and more customizable.
However, running them requires specific libraries installed on your application server. Additionally, integrating them into an existing system can be challenging, and they consume more server resources, such as RAM and CPU.
A cloud-based WAF is the easiest to implement. A third-party service provider is responsible for providing or managing hardware resources and filtering the web application’s traffic. A DNS traffic redirect is required to filter traffic through the WAF, making its implementation straightforward and fast.
Additionally, cloud-based WAFs are cost-effective because they’re subscription-based, where you’re charged monthly or annually. Furthermore, these third parties possess the latest threat intelligence, allowing them to recognize and prevent new application security threats. However, customization options may be limited compared to host-based WAFs.
WAF Versus Firewall
The significant distinction between a WAF and a traditional firewall is that the former covers the network and transport levels (layers three and four). At the same time, the latter protects the application layer (layer seven). In other words, firewalls safeguard a computer network by filtering incoming data packets and controlling network access by allowing or rejecting entry.
WAFs, in contrast, are similar to proxy firewalls. They’re designed to secure application logic/data by ensuring that HTTP/HTTPS servers and applications are protected against threats. They’re a different type of firewall, defined by their methods of filtering data packets and their focus on application-level security.
- Web application firewalls (WAFs) are firewalls that monitor, filter, and block HTTP traffic both to and from a web service.
- WAFs sit between clients and web applications. They monitor and analyze all HTTP communication between both parties to detect malicious data packets before the traffic reaches the web application.
- WAFs protect web applications by constantly monitoring for potential threats. By implementing a WAF, you can prevent third parties from accessing your application and its sensitive data.
- WAFs come in three types: hardware-based (a layer of security between the devices inside and outside of an organization’s network), host-based (runs on servers and can be integrated into your application’s software), and cloud-based (a subscription-based, third-party-provided WAF).
- Firewalls and WAFs, while similar, serve very different purposes. Traditional firewalls protect computer networks, while WAF focuses solely on web-based threats and attacks at the application layer.