Web application firewalls promise protection against common web attacks. Deploy one, enable it, and your applications are safe. That’s the theory. Reality proves far messier.
WAFs sit between users and web applications, inspecting HTTP traffic for malicious patterns. They block SQL injection attempts, cross-site scripting, and other attack vectors. But only when configured properly.
Default configurations provide minimal protection. Vendors ship WAFs in monitoring mode, logging threats without blocking them. Organisations deploy these defaults into production, assuming they’re protected. Attacks sail through unimpeded.
Rule sets require constant tuning. Initial deployments generate massive false positive rates. Legitimate traffic gets blocked, breaking application functionality. Under pressure to restore service, administrators weaken rules or create broad exceptions. Those exceptions become attack vectors. Professional web application penetration testing identifies gaps in WAF protection that attackers could exploit.
Bypass techniques evolve constantly. Attackers study WAF rule sets, finding creative ways to encode malicious payloads that slip past filters. Case variation, encoding schemes, and creative use of allowed characters all enable bypasses.
William Fieldhouse, Director of Aardwolf Security Ltd, notes: “WAFs provide valuable defence in depth, but they’re not silver bullets. During penetration tests, we regularly bypass WAF protections through encoding variations or by exploiting overly permissive exception rules that administrators created to fix false positives.”
SSL/TLS termination creates blind spots. If your WAF doesn’t decrypt HTTPS traffic, it can’t inspect encrypted requests. Attackers send encrypted payloads that the WAF passes through uninspected. The backend application receives malicious input without any filtering.
IP reputation blocking sounds effective. Block requests from known malicious IP addresses and you stop attacks. Except attackers rotate through countless IP addresses, use compromised legitimate systems, or route through cloud services with good reputations.
Rate limiting prevents brute force attacks in theory. Practice reveals complications. Legitimate users behind corporate proxies appear as single IP addresses. Aggressive rate limiting blocks entire organisations. Relaxed rate limiting allows attacks to succeed.
Custom applications require custom rules. Generic WAF rule sets target common vulnerabilities. Your bespoke application has unique attack surfaces that generic rules miss. Custom rule development demands deep understanding of both your application and WAF capabilities.
Logging alone provides little value. WAFs generate enormous volumes of logs. Without proper analysis and alerting, those logs sit unused. Integration with your SIEM and regular review of blocked requests help tune rules and detect sophisticated attacks. When you request a penetration test quote, ensure the assessment includes testing WAF effectiveness against real-world attack techniques.
Virtual patching offers temporary protection for unpatched vulnerabilities. A WAF rule can block exploitation attempts while you test and deploy proper patches. This works only if you create effective rules quickly and monitor them closely.
