Subdomain Takeover

Check for dangling subdomains

A subdomain takeover happens when a subdomain’s DNS still points to a service, a cloud host, a platform, that has been decommissioned, letting someone claim that service and control content on your subdomain. This checker helps you find such dangling DNS entries on your own domains.

Why dangling DNS is a risk

When you stop using a hosted service but leave the DNS record pointing at it, the underlying resource can sometimes be re-registered by someone else, who then serves content from your subdomain, which carries your domain’s trust. This is used for phishing and to bypass protections that trust your domain. It is easy to create by forgetting to remove a DNS record during cleanup.

The defence

The defence is DNS hygiene: remove DNS records when you decommission the service they point to, and audit periodically for records pointing at unclaimed resources. Checking for dangling entries catches them before someone else does. This is for defensive assessment and education around systems you own or protect, or for authorised security testing and awareness, not for targeting others. It runs entirely in your browser, so nothing you enter is uploaded, which matters when the input concerns your own security posture.

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