What a WAF is and what it blocks
A Web Application Firewall (WAF) sits between your visitors and your web application, inspecting every incoming request and deciding whether to allow, block or challenge it. Unlike a traditional network firewall that only looks at IP addresses and ports, a WAF understands the actual web traffic — the URLs, headers, cookies and form data — so it can catch attacks aimed at your application itself.
It is built to stop the most common web threats: SQL injection (tricking your database), cross-site scripting or XSS (injecting malicious scripts), path traversal, and malicious or abusive bots. Its rule sets typically follow the OWASP Top 10, the industry list of the most critical web application risks.
How a WAF actually works
When a request arrives, the WAF evaluates it against a set of rules before it reaches your app. Those rules combine known attack signatures (patterns for SQL injection, XSS and similar), reputation data (known-bad IPs and botnets), and behavioural limits like rate limiting to slow down brute-force and scraping. Based on the result it allows the request, blocks it, or challenges it (for example with a check that separates humans from bots).
Because it operates at Layer 7, the WAF can make decisions a network firewall cannot — for instance, allowing normal traffic to a login page while blocking a request that carries an injection payload. Good WAFs let you run rules in a monitor mode first, so you can see what would be blocked before you enforce it.
Edge WAF vs origin: why placement matters
A WAF that runs at the CDN edge inspects and blocks bad requests at the network's outer layer — close to the attacker and far from your server. Malicious traffic is dropped before it ever consumes your origin's CPU, database or bandwidth, and the same edge that filters attacks also absorbs volumetric DDoS floods across its global capacity.
A WAF that only runs on your own server (or as a plugin) still has to receive and process every request first, so attacks and floods reach your infrastructure before being filtered. Placing security at the edge means your server spends its resources on real visitors, not on fighting off attacks.
Tuning: security without false positives
The hard part of any WAF is blocking attacks without blocking real customers. Overly strict rules can flag legitimate form submissions or API calls as attacks (a false positive), while loose rules let threats through. The practical approach is to start in monitor mode, watch what the rules would catch, then tighten them and add allowlists for the specific paths or parameters your app needs.
This tuning is ongoing work, which is why a managed WAF is valuable: the rules, signatures and DDoS thresholds are maintained for you and updated as new threats appear, so you get protection without having to become a security engineer.
When a WAF matters most
Anywhere users submit data — checkout, contact forms, login — is a target for injection and credential attacks a WAF is built to stop.
A WAF blocks scrapers, credential stuffing and spam bots that steal content and waste your server resources.
An edge WAF paired with DDoS protection keeps you online during floods by filtering and absorbing traffic before it reaches you.
WAF FAQ
What is the difference between a WAF and a regular firewall?
A network firewall filters traffic by IP address and port (Layers 3-4). A WAF works at the application layer (Layer 7): it understands HTTP requests and blocks app-level attacks like SQL injection and XSS that a network firewall cannot see.
Do I need a WAF if I already have SSL/HTTPS?
Yes — they do different jobs. SSL/TLS encrypts traffic so it cannot be read in transit; a WAF inspects that traffic for attacks. An encrypted request can still carry an injection payload, which is exactly what the WAF is there to catch.
Will a WAF slow down my site?
An edge WAF adds negligible latency and can even make your site faster by dropping junk traffic before it reaches your server. It runs alongside the CDN cache, so legitimate visitors are still served from the edge.
Will a WAF block real visitors?
A well-tuned WAF minimizes false positives by starting in monitor mode and using allowlists for your app’s legitimate paths. A managed WAF handles this tuning and keeps the rules current so real customers get through.