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How Cloudflare Works: A Security Blueprint

Jason J. Boderebe
4 min read
#cloudflare #security #cdn #ddos #ops
How Cloudflare Works: A Security Blueprint

Welcome back!

When securing or testing websites, Cloudflare is a name you’ll often encounter. It protects about 19.3% of websites worldwide, with its primary product being DDoS protection, alongside Content Delivery Network (CDN) services and a suite of Internet security tools.

If you want to defend a site or probe its protections, you first need to understand how Cloudflare operates. In this tutorial, I will break down how Cloudflare works from a security perspective. In a later post, I will explore how to test or enhance its defenses.

Let’s get started!

What Is Cloudflare?

Cloudflare is like a digital “bouncer” and performance booster for millions of websites. It sits between users and web servers, filtering traffic, speeding up delivery, and protecting against attacks.

If you want to master modern web security or test it you need to know how Cloudflare works.

Step 1: DNS and Proxy Magic

When a website uses Cloudflare, its domain’s nameservers are pointed to Cloudflare, making it the authoritative DNS provider. Here’s the trick:

  • For proxied records, Cloudflare responds with its own anycast IP addresses-not the real IP of the origin server.
  • All user requests hit Cloudflare’s global edge network first, then get relayed to the actual server.

Result: The origin server’s IP is hidden, and all traffic passes through Cloudflare’s security filters.

Step 2: CDN——Speed and Stealth

Cloudflare operates a content delivery network (CDN) with data centers in over 330 cities.

  • It caches static content (like images, scripts, etc.) at edge locations, serving users from the nearest node.
  • This cuts latency, reduces server load, and makes DDoS attacks less effective.

To test Cloudflare’s protections, you’ll need to uncover the website’s actual IP.

Step 3: Security——The Shield Wall

Cloudflare’s security toolkit includes:

  • DDoS Protection: Detects and blocks floods of malicious traffic using real-time analysis and dynamic rules.
  • Web Application Firewall (WAF): Stops SQL injection, XSS, CSRF, and other web attacks with managed rulesets that are regularly updated.
  • SSL/TLS Encryption: Automatically issues and manages certificates, encrypting traffic between users and Cloudflare, and optionally between Cloudflare and the origin server.
  • Access Control: Limits access to sensitive site areas with multi-factor authentication and IP whitelisting.
  • DNSSEC: Prevents DNS spoofing and cache poisoning attacks.

Step 4: DDoS Mitigation——How the Giant Fights Back

Cloudflare’s DDoS systems operate by:

  • Sampling and analyzing traffic for patterns (source IP, protocols, HTTP headers, error rates).
  • When attack traffic is detected, Cloudflare generates a real-time fingerprint and applies mitigation rules globally-blocking, challenging, or rate-limiting malicious requests.
  • Legitimate users pass through; attackers get blocked or face CAPTCHAs.

Security Note: Cloudflare’s rules are dynamic and ephemeral, meaning its defenses adapt in real time.

Step 5: Edge Computing

Cloudflare isn’t just a shield-it’s also an edge platform.

  • You can run JavaScript code (Cloudflare Workers) at the edge, close to users.
  • This enables custom logic, instant redirects, or even serverless apps-without touching the origin server.

Why does this matter?

  • For defenders: You can block, log, or modify traffic before it reaches your server.
  • For testers: You need to probe both the edge and the origin for vulnerabilities.

How to Spot and Test Cloudflare

  • Check DNS:
    • Use dig or nslookup-if the domain resolves to Cloudflare IPs (104.x.x.x, 172.x.x.x), the site is behind Cloudflare.
  • Bypass Attempts:
    • Try to find the origin IP (historical DNS, email headers, subdomains, direct IP leaks).
    • Test for unproxied subdomains or services.
  • WAF Testing:
    • Send common attack payloads (SQLi, XSS) and check for custom error pages or CAPTCHAs.
  • DDoS Testing:
    • Simulate traffic spikes (legally, with tools like LOIC) and observe Cloudflare’s response (rate limiting, blocks, challenges).

Summary

Cloudflare is a global proxy, CDN, and security platform that protects websites from attacks and speeds up content delivery. To defend or test a site’s security, you must first understand how Cloudflare operates. In an upcoming tutorial, we’ll cover ways to enhance Cloudflare’s protections or probe its defenses.

Stay curious!