What is a Web Application Firewall (WAF)

What is a WAF

A Web Application Firewall (WAF) is a security tool that monitors, filters, and blocks HTTP/HTTPS traffic between web applications and the internet. It acts as a protective barrier specifically designed to defend web applications from various cyber attacks.

When should I use a WAF – is it something I should use?

Whether you should use a WAF depends on your specific situation, but here are the key scenarios where a WAF is highly recommended:

You Should Definitely Use a WAF If:

• You handle sensitive data – Payment information, personal data, healthcare records, or any regulated data
• You run e-commerce or business-critical applications – Downtime or breaches would significantly impact revenue
• You’re subject to compliance requirements – PCI DSS, HIPAA, SOX, or other regulations often require WAF-like protections
• You have public-facing web applications – Any website or API accessible from the internet faces constant attack attempts

Strong Indicators You Need One:

• Your application is connected to a SQL-server
• Your application processes user input (forms, uploads, APIs)
• You’re seeing suspicious traffic or attack attempts in your logs
• Your development team can’t immediately patch every security vulnerability
• You’re running legacy applications or third-party software with known issues
• You want detailed security monitoring and alerting

When WAF Might Be Lower Priority:

• Static websites with no user interaction or data processing
• Internal applications only accessible on private networks
• Very simple applications with minimal attack surface
• Development or testing environments (though still useful)

How WAFs Work

WAFs operate by examining HTTP requests and responses according to predefined security rules. Unlike traditional network firewalls that filter traffic based on IP addresses and ports, WAFs analyze the actual content of web traffic, including:

• Request headers and parameters
• POST data and form submissions
• Cookies and session information
• File uploads
• URL patterns

Key Protection Features

Common Attack Prevention

• SQL injection attacks
• Cross-site scripting (XSS)
• Cross-site request forgery (CSRF)
• DDoS attacks (application layer)
• Brute force attacks
• Path traversal attempts
• Command injection

Traffic Filtering

• Rate limiting to prevent abuse
• Geolocation blocking
• IP reputation filtering
• Bot detection and mitigation

Types of WAFs

Cloud-based WAF: Hosted by a third-party provider (like Cloudflare, AWS WAF, or Azure WAF)
Network-based WAF: Hardware appliances installed on-premises
Host-based WAF: Software installed directly on web servers

Benefits of using a WAF

WAFs provide real-time protection without requiring changes to your application code, offer detailed logging for security analysis, and can help with regulatory compliance requirements. They’re particularly valuable for protecting web applications that may have vulnerabilities or legacy systems that can’t be easily updated.

Further reading

• https://en.wikipedia.org/wiki/Web_application_firewall