Subdomain takeover remains one of the most underappreciated attack vectors in enterprise security. When an organization decommissions a cloud resource but forgets to clean up the DNS record pointing to it, that dangling record becomes an open invitation for attackers to claim the subdomain and serve content under the organization's domain.
Beyond CNAME: Expanded Takeover Vectors
While CNAME-based takeovers targeting services like GitHub Pages, Heroku, and AWS S3 are well-documented, our research identified underexplored vectors through NS delegation and MX record takeovers. NS delegation takeovers are particularly dangerous: if an organization's subdomain delegates DNS resolution to a nameserver that can be claimed (such as an expired AWS Route53 hosted zone), an attacker gains complete control over all DNS records for that subdomain, enabling them to issue TLS certificates via DNS-01 challenges.
Our Automated Discovery Pipeline
We built an automated pipeline that processes enterprise attack surfaces at scale. The system performs continuous subdomain enumeration using certificate transparency logs, DNS brute-forcing, and passive DNS databases. Each discovered subdomain is then tested against our fingerprint database of over 80 vulnerable service configurations, including cloud providers, SaaS platforms, and CDN services.
Validation is the critical differentiator. Rather than simply flagging potential takeovers, our system actively validates exploitability by checking service registration availability, verifying DNS propagation timing, and confirming that the claimed resource would be served under the target domain. This eliminates false positives that plague simpler tools.
Case Studies
In a recent engagement, we discovered 23 takeover-vulnerable subdomains across a Fortune 500 company's attack surface. These included an abandoned Azure CDN endpoint serving a customer-facing application, an expired Fastly configuration on a marketing subdomain, and a decommissioned Shopify store that could be claimed to phish employees via SSO redirect manipulation. Strobes EASM continuously monitors your entire attack surface for dangling DNS records and subdomain takeover opportunities.