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Glossary Term

Zombie Subdomains

Forgotten subdomains that still exist in DNS invite takeover attempts.

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Zombie Subdomains

1-minute read

What it is

Zombie Subdomains are inactive or forgotten subdomains that still point to decommissioned services, third-party apps, or cloud resources.

Why it matters

They are prime targets for subdomain takeover attacks, letting adversaries host malicious content or harvest credentials under a trusted domain.

How to reduce risk

  • Continuously scan DNS records and certificate transparency logs for stale subdomains
  • Remove unused subdomains or update DNS when services are retired
  • Automate checks whenever infrastructure or SaaS resources are decommissioned

Related Terms: Subdomain Takeover, Dangling DNS Record, Attack Surface Discovery

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