Web Application Firewall (WAF)

A WAF is a security solution that monitors, filters, and blocks HTTP traffic to and from a web application based on a set of rules to protect against web attacks.

A Web Application Firewall operates at the application layer (Layer 7) to protect web applications from common attacks.

WAF protection against: - SQL injection - Cross-site scripting (XSS) - Cross-site request forgery (CSRF) - Remote file inclusion - XML attacks - Bot attacks and scraping

WAF deployment models: - Cloud WAF: Cloudflare, AWS WAF, Azure WAF - On-premise appliances: F5, Imperva - Host-based: ModSecurity - CDN-integrated: Automatic with CDN providers

Rule modes: - Blocking: Actively blocks malicious requests - Detection: Logs but doesn't block - Learning: Builds baseline of normal traffic

Why It Matters

WAFs provide critical protection against automated web attacks—SQL injection, XSS, and other OWASP Top 10 vulnerabilities—that remain the primary vectors for web application breaches. PCI DSS requirement 6.6 specifically mandates either a WAF or regular application security assessments. Cloud-based WAFs have made this protection accessible to organizations of all sizes, providing enterprise-grade web application security with minimal deployment effort.

Key Points

Protects against OWASP Top 10 attacks

Cloud WAFs are easiest to deploy

Requires tuning to reduce false positives

Not a replacement for secure coding

Often required for PCI DSS compliance

Applicable Compliance Frameworks

PCI DSS SOC 2 ISO 27001

Related Terms

OWASP Top 10

OWASP Top 10 is a regularly updated list of the most critical web application security risks, serving as a standard for application security testing.

Firewall

A firewall is a network security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules.

API Security

API security encompasses practices and technologies used to protect Application Programming Interfaces from attacks and misuse, including authentication, authorization, rate limiting, and input validation.