---
name: cdn-peek
description: Lightweight check for whether a CDN/WAF-fronted host is reachable outside its edge, using only dig, curl, openssl, whois, and nc - no API keys, no paid tools, no brute-force scans. Works against any reverse-proxy edge (Cloudflare, CloudFront, Akamai, Fastly, Sucuri, Imperva/Incapsula, Azure Front Door, Google Cloud CDN, Gcore, Bunny, Edgio). Use for authorized security testing of a host you own or are engaged to assess - when asked to "find the origin", "bypass the CDN/WAF", "check if the origin leaks", "is this behind Cloudflare/CloudFront", or to map a domain's non-fronted surface. Produces a check/done ledger and, if found, a confirmed origin IP.

---

## Scope & authorization

Only run against hosts the user owns or is contractually engaged to test. This is origin discovery for defensive hardening (confirming the edge actually hides the origin), not for attacking third parties. If the target isn't clearly the user's or in-scope, ask before probing.

This skill is deliberately dependency-free: every step is a plain `dig`, `curl`, `openssl`, `whois`, or `nc` one-liner. It covers origin reachability, not WAF signature evasion (payload encoding / rule bypass) - that is a separate discipline. Techniques that need API keys or heavy tooling (favicon-hash pivots on Shodan/Censys/ZoomEye/FOFA, historical-DNS via SecurityTrails, passive-source or brute-force subdomain enumeration, app-callback/SSRF leaks) are intentionally out of scope here; note them as unrun if the target warrants a deeper pass.

## Step 0 - identify the edge

Match the host's IPs/NS/CNAME against known edge fingerprints, then load that provider's client-IP header. Everything after is provider-agnostic; only the IP ranges and the client-IP header name differ.

| Edge | Fingerprint (IP/NS/CNAME) | Client-IP header |
|---|---|---|
| Cloudflare | 104.16/13, 172.64/13, 2606:4700::/32, *.ns.cloudflare.com | CF-Connecting-IP |
| CloudFront | *.cloudfront.net, AWS CLOUDFRONT ranges | CloudFront-Viewer-Address |
| Akamai | *.akamaiedge.net, *.akamai.net, *.edgekey.net | True-Client-IP |
| Fastly | *.fastly.net, 151.101/16 | Fastly-Client-IP |
| Sucuri | *.sucuri.net, 192.88.134/23, 185.93.228/22 | X-Sucuri-ClientIP |
| Imperva/Incapsula | *.incapdns.net | Incap-Client-IP |
| Azure Front Door | *.azurefd.net, AzureFrontDoor.Backend tag | X-Azure-ClientIP |
| Google Cloud CDN | Google ranges, ghs.googlehosted.com | X-Forwarded-For |
| Gcore / Bunny / Edgio | *.gcdn.co, *.b-cdn.net, *.edgecastcdn.net | X-Forwarded-For |

## Methodology (run in order; each step is a check with a done/result state)

1. **Confirm fronted.** `dig` A/AAAA/NS/CNAME, match IPs against the edge ranges from Step 0. If not fronted, stop - there's nothing to bypass.
2. **DNS record sweep.** `dig` A/AAAA/CNAME/TXT/MX/SOA/SRV/CAA and `_dmarc`. SPF `ip4:`/`include:`, MX, and autodiscover records frequently name a non-fronted origin or mail IP.
3. **CT lookup (free, no key, no brute).** One `curl` to crt.sh and certspotter for `*.domain`: enumerates subdomains and the host's own cert history. Flag any subdomain resolving to a non-edge IP; a Let's Encrypt / self-issued cert scoped to just the target host (not the edge's shared cert) is a pivotable leak.
4. **Fingerprint every non-edge IP.** `dig -x` (reverse DNS), `whois` (ASN/hosting org), `curl` banner, `openssl s_client` cert CN/SAN/issuer. Reveals the hosting footprint even when the box isn't the origin.
5. **Host-confusion.** `curl --resolve target:443:<IP>` with the target Host + SNI against each non-edge IP; compare title/body/length to the real fronted response. Same content = origin bypass; different (default vhost) = not the origin.
6. **Response-header & error-page leak.** `curl -I` the target and a bogus path; inspect `Via`, `X-Cache`, `X-Served-By`, `X-Backend-Server`, `Server`, `X-Powered-By`, redirect `Location`, and verbose error bodies for internal hostnames or RFC1918/origin IPs.
7. **Client-IP header trust.** Send `X-Forwarded-For`, `X-Real-IP`, and the edge's own client-IP header (Step 0) = `127.0.0.1`; compare responses. Bypasses IP allowlist/geo/rate-limit logic - not the origin. A hardened edge rejects a client-supplied copy of its own header (Cloudflare answers 403 `error code: 1000`); if the app instead trusts it, that is the finding.
8. **Edge header tricks.** `X-Forwarded-Host`, `X-Original-URL`, blank/mismatched `Host` - test for cache/redirect poisoning, routing bypass, and header reflection in links.
9. **Confirm candidate origin.** For any candidate IP from steps 2/3/4: `curl -skI --resolve target:443:<IP>`. If it returns the target app and isn't firewalled to the edge ranges, it's a full bypass.
10. **Port check on a confirmed origin.** `nc -z` the non-HTTP services the edge never proxies (SSH/22, k8s API/6443, kubelet/10250, DB/admin ports).

## Runnable snippets

```bash
# 1 confirm fronted
dig +short TARGET A; dig +short TARGET AAAA; dig +short DOMAIN NS; dig +short TARGET CNAME
# 2 DNS sweep
for t in A AAAA CNAME TXT MX SOA SRV CAA; do echo "$t: $(dig +short TARGET $t | tr '\n' ' ')"; done; dig +short _dmarc.DOMAIN TXT
# 3 CT lookup (subdomains + cert history, no key)
curl -s "https://crt.sh/?q=%25.DOMAIN&output=json" | python3 -c "import sys,json;print('\n'.join(sorted({n for x in json.load(sys.stdin) for n in x['name_value'].split(chr(10))})))"
curl -s "https://api.certspotter.com/v1/issuances?domain=DOMAIN&include_subdomains=true&expand=dns_names" | python3 -c "import sys,json;[print(n) for x in json.load(sys.stdin) for n in x.get('dns_names',[])]" | sort -u
# 4 fingerprint a non-edge IP
dig -x IP +short; whois IP | grep -iE 'orgname|netname|origin|as[0-9]'; echo | openssl s_client -connect IP:443 -servername TARGET 2>/dev/null | openssl x509 -noout -subject -issuer -ext subjectAltName
# 5 host-confusion
curl -sk --resolve TARGET:443:IP https://TARGET/ | python3 -c "import sys,re;h=sys.stdin.read();t=re.search(r'<title>(.*?)</title>',h,re.S);print('title:',t and t.group(1).strip(),'len:',len(h))"
# 6 header / error leak
curl -sI https://TARGET/ | grep -iE 'via|x-cache|x-served-by|x-backend|server|x-powered|location'
curl -sk https://TARGET/nonexistent-$RANDOM | grep -oiE '([0-9]{1,3}\.){3}[0-9]{1,3}|[a-z0-9.-]+\.(internal|local|lan)'
# 7 client-IP header trust  (swap EDGE_HEADER for the provider's own, from Step 0)
for h in "X-Forwarded-For: 127.0.0.1" "X-Real-IP: 127.0.0.1" "EDGE_HEADER: 127.0.0.1"; do echo "[$h] $(curl -sk -o /dev/null -w '%{http_code} %{size_download}b' -H "$h" https://TARGET/)"; done
# 8 edge header tricks
for h in "X-Forwarded-Host: evil.example" "X-Original-URL: /admin" "Host: example.com"; do echo "[$h] $(curl -sk -o /dev/null -w '%{http_code} %{size_download}b' -H "$h" https://TARGET/)"; done
# 9 confirm candidate origin
curl -skI --resolve TARGET:443:CANDIDATE_IP https://TARGET/ | head
# 10 port check
for p in 22 6443 10250 3306 5432 8080 8443; do nc -z -G2 CANDIDATE_IP $p 2>/dev/null && echo "open $p"; done
```

## Output

Finish with a `check / done? / result` ledger over all 10 steps, then a one-line verdict:
- **Clean** - every check exhausted and negative; origin not leaking via DNS/cert/header/edge.
- **Exposed** - a confirmed origin IP (name the step that found it and the confirming direct fetch), plus the fix (firewall origin to the edge ranges only, enable origin authentication such as Cloudflare Authenticated Origin Pulls or CloudFront custom-header validation, strip client-IP headers at the edge).

Report each step's true status - done or not-run - so coverage is honest; never present an unrun step as clean.