Cloudflare Hardening

Cloudflare Hardening

Cloudflare gives you a powerful edge layer for free, but its defaults are conservative — most of the protection is opt-in. This skill walks the security-relevant settings and the ones that catch people out.

Applies to Cloudflare's main product (DNS + Proxy + WAF + Workers/Pages/R2). Not Magic Transit / Spectrum specifics.

When to invoke

• Domain just onboarded to Cloudflare
• Site behind CF was scraped, brute-forced, or DDoSed
• Origin IP may be exposed (showed up in dnshistory, accidentally A-recorded)
• Periodic review of an existing public site
• Setting up Cloudflare Pages or R2 with a custom domain

Step 1 — Lock the account itself

Before site settings, harden the account.

• 2FA on the account with WebAuthn / hardware key, not SMS
• API tokens, not Global API Key — Global API Key has account-wide power and cannot be scoped
• Audit Logs — Account → Audit Log shows who did what; review monthly
• Members — separate humans from automation; each automation gets its own scoped token

API tokens: scope to specific zones + specific permissions. A common mistake is creating a "DNS edit" token at account level when only one zone needs it.

Step 2 — DNS and proxy posture

Zone → DNS → Records

• All public hostnames proxied (orange cloud) unless you have a specific reason for grey-cloud (e.g. mail records — MX must be grey)
• Origin IP must not be in any public DNS record — common leaks:
• Direct A record for direct.example.com or origin.example.com left over
• MX pointing to a host on the same IP as the web origin (move mail to a separate IP/host)
• SPF/TXT records containing IP literals that match the origin
• DNSSEC — enable in DNS → Settings. Requires DS record at the registrar.
• CAA records — restrict who can issue certs for your domain. Cloudflare adds these automatically if you turn it on.

If your origin IP is known-leaked, rotate it — provider panel usually lets you re-assign. Pair with origin allowlist (next step).

Step 3 — Origin allowlist (defense-in-depth)

Cloudflare proxy is useless if attackers can hit the origin IP directly. Two complementary controls:

1. Authenticated Origin Pulls — origin only accepts TLS connections that present Cloudflare's client cert.

Zone → SSL/TLS → Origin Server → Authenticated Origin Pulls

Then on your origin nginx:

ssl_client_certificate /etc/ssl/cloudflare/authenticated_origin_pull_ca.pem;
ssl_verify_client on;

2. Firewall the origin to Cloudflare's IPs only — at the VPS, restrict 80/443 to CF's published ranges:

# Fetch and ufw-allow only Cloudflare IPs (refresh on a cron)
sudo ufw delete allow 80/tcp
sudo ufw delete allow 443/tcp
for ip in $(curl -s https://www.cloudflare.com/ips-v4); do
  sudo ufw allow from "$ip" to any port 80,443 proto tcp comment 'cloudflare'
done
for ip in $(curl -s https://www.cloudflare.com/ips-v6); do
  sudo ufw allow from "$ip" to any port 80,443 proto tcp comment 'cloudflare-v6'
done
sudo ufw reload

Either alone is acceptable; both is best. Without one of them, the proxy provides little hardening because attackers will bypass it.

Step 4 — TLS

Zone → SSL/TLS

• Encryption mode: Full (strict) — anything less either allows MITM (Full, not strict) or runs plaintext between CF and origin (Flexible). Flexible is a footgun; do not use.
• Minimum TLS Version: 1.2 minimum, 1.3 if your audience tolerates it
• Always Use HTTPS: on
• Automatic HTTPS Rewrites: on
• HSTS — apply via Edge Certificates → HSTS. max-age=31536000, includeSubDomains, preload only if you understand the lock-in.

Step 5 — WAF and Bot management

Zone → Security → WAF

• Managed Rules → Cloudflare Managed Ruleset: on, default action Managed Challenge
• OWASP Core Ruleset: on, but watch for false positives — start in Log mode, then escalate
• Custom Rules for your stack:

# Block direct access to wp-admin from outside your country (adjust)
(http.request.uri.path contains "/wp-admin" or http.request.uri.path contains "/wp-login.php")
  and ip.geoip.country ne "AT"
→ Action: Managed Challenge

# Block known abusive paths
http.request.uri.path in {"/.git/config" "/.env" "/wp-config.php.bak" "/server-status"}
→ Action: Block

# Tighten login endpoints
http.request.uri.path eq "/wp-login.php" and http.request.method eq "POST"
→ Action: Managed Challenge

# Hide xmlrpc unless you actually use it
http.request.uri.path eq "/xmlrpc.php"
→ Action: Block

• Bot Fight Mode (free tier): on. Catches dumb scrapers. False positives are rare.
• Super Bot Fight Mode (paid): better, distinguishes verified bots from definitely-automated traffic.
• Rate Limiting Rules — free tier gives one rule; use it well:

http.request.uri.path eq "/wp-login.php" → 5 requests / 1 minute per IP → Block 10m

Step 6 — Security headers via Transform Rules

You can inject headers without touching the origin. Rules → Transform Rules → Modify Response Header:

Set: Strict-Transport-Security  =  max-age=31536000; includeSubDomains
Set: X-Content-Type-Options     =  nosniff
Set: Referrer-Policy            =  strict-origin-when-cross-origin
Set: Permissions-Policy         =  camera=(), microphone=(), geolocation=(), interest-cohort=()
Set: Content-Security-Policy    =  

CSP is too app-specific to template here. Start in Content-Security-Policy-Report-Only with a permissive baseline, watch the reports for a week, tighten, then promote to enforcing.

Step 7 — Zero Trust Access for admin paths

/wp-admin, /admin, /staging, /api/internal/* should not be reachable from the open internet for most projects. Cloudflare Zero Trust (free for ≤ 50 users) gives you SSO-gated access:

Cloudflare Zero Trust → Access → Applications → Add → Self-hosted

• Application domain: *.example.com/wp-admin*
• Identity provider: Google/GitHub/email-OTP
• Policy: Allow → emails in @yourcompany.com or specific list

Now /wp-admin requires SSO before traffic reaches the origin at all. Brute-force on the WP login endpoint stops being your problem.

Step 8 — Cache and Page Rules

(New zones: Page Rules are being phased out in favor of Cache Rules, Configuration Rules, Origin Rules, and Single Redirects.)

• Cache static assets aggressively, but never cache responses with Set-Cookie or auth headers
• Bypass cache for /wp-admin/*, /wp-login.php, /cart/*, /checkout/*, /api/* — auth and per-user content
• Always Use HTTPS as a Configuration Rule, not a workaround
• Single Redirect is the modern replacement for the "forward url" Page Rule

Step 9 — Cloudflare Pages security

If you use Pages:

• Branch deploy previews are public by default — gate them with Access if they contain anything non-public
• Environment variables marked as Secret are not exposed to client bundles, but NEXT_PUBLIC_* and similar prefixes still go to the browser. Audit which env vars exist and where they end up.
• _headers file in the output directory applies headers per path — convenient for static-site CSP
• Custom domain CNAME must be a CF-orange-clouded record on a CF-managed zone

Step 10 — R2 buckets

• Public buckets — only for content actually meant to be public. Check Bucket → Settings → Public access.
• Custom domain on R2 — use it for public assets; never bind sensitive buckets to public custom domains
• CORS — restrict origins, do not use * unless you understand it
• Object listing — disable public listing; serve specific objects, not directory enumeration

Step 11 — Audit and monitoring

Zone → Security → Events
Zone → Analytics → Security

• Review weekly for the first month, then monthly
• Look for: unusual ASNs, sustained 4xx/5xx from one source, spikes in Managed Challenge issuances
• For paid tiers: alerts on rule actions, expensive queries to Workers

Step 12 — Periodic re-audit

Once a quarter, walk through:

• [ ] All DNS records still in use; remove orphans
• [ ] No DNS record exposes origin IP
• [ ] Authenticated Origin Pulls + origin firewall still in place
• [ ] WAF rules still match current app paths
• [ ] CSP still matches frontend (after deploys it can drift)
• [ ] No new public R2 buckets without intent
• [ ] No new long-lived API tokens with broad scope; rotate ones older than 90 days
• [ ] Zero Trust app list matches current team

What this skill will not do

• Recommend Flexible SSL or any setting that allows plaintext between CF and origin
• Help bypass Cloudflare protection on a site you do not own
• Endorse leaving origin IP discoverable when the site is intentionally proxied

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: GoldenWing-360
• Source: GoldenWing-360/claude-security-skills
• License: MIT
• Homepage: https://goldenwing.at

Install and usage instructions live in the source repository linked above.