What is Web Application Firewall (WAF)?
A security layer that monitors, filters, and blocks malicious HTTP traffic to and from a web application. It protects against common attacks like SQL injection, XSS, and DDoS.
In plain English
A WAF is like a smart security guard at a building entrance who checks everyone's credentials AND behavior. Unlike a regular lock (firewall) that just checks if you have a key, the WAF also watches for suspicious behavior — like someone carrying lockpicks or acting nervously.
How it works
A WAF sits between users and your web server, inspecting every HTTP request and response. It uses predefined rules, pattern matching, and sometimes AI/ML to identify and block malicious traffic. It can detect SQL injection attempts, XSS payloads, bot traffic, and other attack patterns. WAFs can be cloud-based (Cloudflare, AWS WAF), host-based, or network-based.
Why it matters for AI-built apps
A WAF provides a crucial safety net for AI-generated code that may contain vulnerabilities. While it shouldn't replace secure coding, it adds a protective layer that can block known attack patterns even if your application code is vulnerable. For AI-built apps that haven't been thoroughly security-reviewed, a WAF is an essential stopgap measure.
Common issues
Over-relying on WAF while ignoring application-level security, false positives blocking legitimate users, misconfigured rules that are too permissive, performance overhead from aggressive rule sets, and not updating WAF rules to address new attack patterns.
Best practices
Use a WAF as a defense-in-depth layer, not your only security measure. Start with managed rule sets from your provider (Cloudflare, AWS). Monitor false positives and tune rules accordingly. Enable logging and review blocked requests regularly. Combine with application-level security measures like input validation and parameterized queries.
Frequently asked questions
Do I need a WAF if my code is secure?
A WAF adds defense-in-depth, which is valuable even for well-coded apps. It protects against zero-day exploits, provides DDoS mitigation, blocks known-bad IP addresses, and catches attacks that slip through application-level defenses. Think of it as insurance — you hope you never need it, but you're glad it's there.
Which WAF should I use?
For most startups, Cloudflare's free tier is an excellent starting point — it includes basic WAF rules, DDoS protection, and CDN. For AWS-hosted apps, AWS WAF integrates well with ALB and CloudFront. Vercel's platform includes basic protection by default. Choose based on your hosting platform and budget.
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