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Introduction:
Digital platforms like Booking.com harvest vast amounts of personal data but repeatedly fail to enforce basic security hygiene—leaving subdomains with “Not Secure” warnings for years. When cybercriminals exploit these unencrypted assets, the result is predictable: stolen credentials, convincing phishing scams, and financial devastation for consumers, all while regulators lag behind in defining and enforcing what “good security” actually means.
Learning Objectives:
- Identify and map exposed, non-HTTPS subdomains using OSINT and DNS enumeration techniques.
- Understand how SSL/TLS misconfigurations and unsecured assets enable account takeover and fraud.
- Implement defensive hardening for subdomains, cloud assets, and API endpoints to prevent data leakage.
You Should Know:
- The Anatomy of a ‘Not Secure’ Subdomain – What It Means and Why It Matters
A “Not Secure” warning in your browser indicates that the connection uses plain HTTP instead of HTTPS, meaning all data (including login credentials, session cookies, and personal information) is transmitted in cleartext. Attackers on the same network can eavesdrop, modify responses, or perform man‑in‑the‑middle attacks. Worse, an unsecured subdomain can be used to host convincing phishing pages that mimic the parent company’s login portal.
Step‑by‑step guide to detect insecure subdomains:
- Linux/macOS: Use `curl -I http://
.booking.com` to check the HTTP response. Look for `Location:` redirects to HTTPS – absence indicates insecurity.</li> <li>Windows: Open PowerShell and run <code>Invoke-WebRequest -Uri http://[bash].booking.com -Method Head</code>. Check the `StatusCode` (200 means plain HTTP served).</li> <li>Browser check: Type `chrome://net-export/` (Chrome) or `about:networking` (Firefox) to log all requests; filter by `http://` to find insecure assets. - Automated scan: Use `nmap -p 80,443 --script http-title [bash]` to identify which subdomains answer on port 80 without redirect.</li> </ul> <ol> <li>Subdomain Enumeration: How Attackers Find Your Weak Spots Before exploiting unsecured subdomains, adversaries discover them using DNS brute‑forcing, certificate transparency logs, and search engines. Andy Jenkinson highlighted that Booking.com left a subdomain "Not Secure" for over three years – a prime target for takeover or impersonation.</li> </ol> <h2 style="color: yellow;">Step‑by‑step enumeration (authorized testing only):</h2> <ul> <li>DNS brute‑force with <code>dnsrecon</code>: </li> </ul> <h2 style="color: yellow;">`dnsrecon -d booking.com -D /usr/share/wordlists/subdomains.txt -t brt`</h2> (Replace with your own target domain after obtaining permission.) - Certificate Transparency logs: `curl -s "https://crt.sh/?q=%.booking.com&output=json" | jq -r '.[].name_value' | sort -u` This reveals all subdomains ever issued a TLS certificate – even those no longer in use. - Google dorks for exposed subdomains: <h2 style="color: yellow;">`site:booking.com -inurl:https` finds pages served over HTTP.</h2> <ul> <li>Windows alternative: Use `nslookup` in a loop: [bash] Get-Content subdomains.txt | ForEach-Object { nslookup $_.booking.com 8.8.8.8 }
- Exploiting Unsecured Subdomains – From Foothold to Full Breach
Once an attacker finds a subdomain serving HTTP, they can perform session hijacking, cookie theft, or deploy a fake login page that captures user credentials. With 28 million users’ data already exploited due to Booking.com’s negligence, this vector is not theoretical.
Step‑by‑step attack simulation (lab environment only):
- Capture HTTP traffic with
tcpdump:
`sudo tcpdump -i eth0 port 80 -A -c 100` – view cleartext data. - Session hijacking using `ferret` &
hamster: Sniff cookies from the unsecured subdomain and replay them in a browser. - DNS spoofing with
ettercap:
`sudo ettercap -T -M arp:remote /target_IP// /gateway_IP// -P dns_spoof`
Redirect users from the legitimate HTTP subdomain to a cloned phishing site. - Mitigation check: Verify HSTS (HTTP Strict Transport Security) header:
`curl -sI https://subdomain.example.com | grep -i “strict-transport-security”` – missing header means the site can be downgraded to HTTP.
- Cloud Hardening: Securing Subdomains in AWS, Azure, and GCP
Many “Not Secure” subdomains point to cloud storage buckets or load balancers that were never configured for HTTPS. A misconfigured S3 bucket can expose terabytes of user data; an unencrypted Azure CDN endpoint leaks API keys.
Step‑by‑step cloud subdomain hardening:
- AWS: Enforce HTTPS on S3 buckets via bucket policy:
{ "Effect": "Deny", "Principal": "", "Action": "s3:GetObject", "Condition": {"Bool": {"aws:SecureTransport": "false"}}, "Resource": "arn:aws:s3:::your-bucket/" } - Azure Storage: Enable “Secure transfer required” in the Azure portal or via CLI:
`az storage account update –name mystorageaccount –https-only true`
- GCP Cloud Storage: Add `–require-https` to bucket creation:
`gsutil mb -l US –require-https gs://my-bucket`
- Subdomain takeover prevention: Use `dig` to check for dangling DNS records pointing to deprovisioned cloud services:
`dig CNAME insecure-sub.booking.com` – if the target resource no longer exists, an attacker can claim it.
- API Security and Data Leakage – The Booking.com Case
Unsecured subdomains often host APIs that bypass authentication. Attackers can enumerate API endpoints over HTTP, extract user PII, or trigger unauthorized bookings. The 28‑million‑record breach likely involved such exposed interfaces.
Step‑by‑step API testing (on your own infrastructure):
- Discover API endpoints via
gobuster:
`gobuster dir -u http://api-sub.booking.com -w /usr/share/wordlists/api-common.txt`
– Test for CORS misconfiguration:curl -H "Origin: https://evil.com" -I https://api-target.com/endpoint
Look for `Access-Control-Allow-Origin: ` – allows any website to read the response.
- Check for HTTP vs HTTPS redirects on API routes:
`curl -L -s -o /dev/null -w “%{url_effective}\n” http://api.booking.com/v1/user`
If the final URL remains HTTP, the API leaks credentials.
– Windows PowerShell alternative:Invoke-RestMethod -Uri "http://api-sub.booking.com/data" -Method Get
6. Proactive Monitoring with Threat Intelligence
Instead of waiting for a breach, organizations must continuously monitor their own subdomains for missing HTTPS, expired certificates, and rogue lookalike domains. Andy Jenkinson’s call for “transparency and a security revolution” aligns with implementing automated asset discovery.
Step‑by‑step monitoring setup:
– Use SecurityTrails API (free tier) to list all subdomains:
`curl -H “APIKEY: your_key” https://api.securitytrails.com/v1/domain/booking.com/subdomains` - Shodan search for insecure subdomains:
`https://www.shodan.io/search?query=hostname%3Abooking.com+port%3A80` - Automated alerting with
nuclei:
`nuclei -u http://subdomain.booking.com -tags misconfig,http-missing-security-headers`
– Linux cron job to check HSTS daily:echo "GET /" | openssl s_client -connect sub.booking.com:443 -servername sub.booking.com 2>&1 | grep -i "strict-transport-security" || echo "HSTS missing" | mail -s "Alert" [email protected]
- Building a Security Warning System – Inspired by Cigarette Packaging
The post’s core demand is that digital platforms display unavoidable warnings: “Your data may be exposed, and you may be targeted.” While waiting for regulation, developers can implement client‑side warnings and forced HTTPS.
Step‑by‑step implementation:
- Add HTTP response header `Feature-Policy: encrypted-media ‘self’` to warn on insecure origins.
- Deploy `Report-URI` directive:
`Report-To: {“group”:”default”,”max_age”:10886400,”endpoints”:[{“url”:”https://your-csp-endpoint/report”}]}`
Receive browser reports when users try to access HTTP versions. - Enforce HTTPS via `.htaccess` (Apache):
RewriteEngine On RewriteCond %{HTTPS} off RewriteRule ^(.)$ https://%{HTTP_HOST}/$1 [R=301,L] - For Windows IIS: Install URL Rewrite module and add rule to redirect all HTTP traffic to HTTPS.
- User‑facing warning overlay: Inject a JavaScript snippet that checks `window.location.protocol` and displays a red banner if `http:` is used, mimicking the cigarette warning label concept.
What Undercode Say:
- Negligence is predictable: Leaving a subdomain unencrypted for three years is not an oversight – it’s a pattern. Attackers actively scan for such assets because they guarantee low‑effort returns.
- Consumers cannot audit security alone: The burden must shift to platforms, with mandatory third‑party penetration testing and public disclosure of “Not Secure” assets. Regulators need technical depth to enforce real standards, not checkbox compliance.
- Technical hygiene stops the majority of breaches: Forcing HTTPS, HSTS preloading, and automated subdomain takedown would have prevented the Booking.com scenario. These are not advanced tactics – they are basic internet hygiene that costs almost nothing.
Prediction:
Within 24 months, a major data protection authority (e.g., EU’s EDPS or California’s CPPA) will mandate that any platform handling personal data must display a real‑time security posture indicator on every page – similar to the padlock but including subdomain validation and data retention warnings. Companies like Booking.com will face class‑action lawsuits not just for the breach, but for knowingly leaving “Not Secure” subdomains exposed for years. The security revolution driven by user boycotts will force a consolidation of cloud assets and a shift toward zero‑trust subdomain architectures, where every subdomain must prove HTTPS compliance every 24 hours or be automatically quarantined.
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Reported By: Andy Jenkinson – Hackers Feeds
Extra Hub: Undercode MoN
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