Is Your Domain Secure from Subdomain Takeover? Check via API
security #api #domain #subdomaintakeover #defcon #whois #rapidapi #threatintel DEF CON 32 made one thing clear: open-source security chips and hardware keys are having a moment. But while badges get the spotlight, most real-world attacks still start with something far less glamorous — a forgotten DNS record, a dangling CNAME, or a missing DMARC policy. Subdomain takeover remains one of the most reliable paths from "benign misconfiguration" to "account compromise." If your organization owns dozens or hundreds of domains, manual checks do not scale. This is where an API-first domain intelligence tool becomes essential. In this post, we'll use the Domain WHOIS API to automate: WHOIS/RDAP lookups and domain-age checks DNS record enumeration and SSL certificate inspection Subdomain discovery and takeover-risk scoring Email-security validation (SPF, DMARC, DKIM, DNSSEC, MTA-STS) Historical snapshots via /history Why subdomain takeover still matters A subdomain takeover happens when a DNS record points to a third-party service — GitHub Pages, Heroku, AWS S3, Vercel, etc. — that is no longer registered under your account. An attacker can claim the dangling endpoint and suddenly serve content under your brand's domain. Bug bounty programs consistently rank subdomain takeovers as high-severity findings because they enable phishing, session hijacking, and reputation abuse. The root cause is usually an orphaned CNAME that nobody is monitoring. The fix is continuous monitoring. Instead of running dig , whois , and openssl by hand, we can consolidate everything into a single API call. What the Domain WHOIS API returns The API combines several data sources into one response: Capability Use case WHOIS via RDAP Ownership, registrar, creation/expiration dates DNS records A, AAAA, CNAME, MX, NS, TXT records SSL certificate Issuer, expiry, SANs, validity Subdomain discovery Asset inventory and shadow-IT detection Takeover risk Dangling CNAME/A-record scoring Email security SPF, DMARC,