A WAF, or Web Application Firewall, is a security solution designed to protect web applications from a wide range of attacks and vulnerabilities. Unlike traditional firewalls that operate at the network level, WAFs operate at the application layer, allowing them to monitor and filter HTTP traffic between a web application and the internet. They inspect incoming requests and outgoing responses, identifying and blocking malicious traffic that could exploit application-level vulnerabilities like SQL injection, cross-site scripting (XSS), and other OWASP Top 10 threats.
The main difference between a firewall and a WAF lies in their scope and purpose. A traditional firewall acts as a barrier between a trusted internal network and untrusted external networks, controlling traffic based on IP addresses, ports, and protocols. It primarily focuses on network-level security, whereas a WAF is specifically designed to protect web applications by analyzing and filtering HTTP traffic at the application layer. WAFs are more granular in their inspection, focusing on the content and structure of web requests and responses to detect and block attacks targeting web applications.
WAF rules define the criteria and conditions under which traffic is allowed or blocked by the web application firewall. These rules can be predefined by security experts or customized based on specific application requirements and security policies. Common WAF rules include pattern matching for known attack signatures, rate limiting to prevent abuse, URL whitelisting or blacklisting, and rules to enforce compliance with security standards like PCI DSS (Payment Card Industry Data Security Standard).
You would use a WAF whenever you need to protect web applications from potential threats and vulnerabilities that could compromise their security. WAFs are particularly valuable in scenarios where web applications handle sensitive data, such as financial information, personal details, or proprietary business data. They provide an additional layer of defense beyond traditional network security measures, ensuring that web applications remain secure against evolving threats without impacting legitimate user traffic.
There are two main types of WAFs: network-based WAFs and host-based WAFs. Network-based WAFs are typically deployed between the client and the web server, acting as a gateway to filter and monitor incoming HTTP/HTTPS traffic. They are well-suited for protecting multiple web applications within an organization’s network but may introduce latency due to their placement. Host-based WAFs, on the other hand, are installed directly on web servers or within the application itself, offering more granular control and visibility into application-layer traffic. They are ideal for environments where individual applications require customized security policies or where compliance requirements mandate application-level protection.