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Application & OT Security · Foundational

Subdomain Enumeration

Discovering subdomains of a target domain to expand the known attack surface.

Definition

Techniques include certificate transparency searches, passive DNS datasets, search engines, brute-forcing with wordlists, and zone transfers. Forgotten subdomains often host outdated or test applications. Tools include Amass, Subfinder, theHarvester and gobuster in DNS mode.

Example

amass enum -passive -d example.com

Exam tip

Certificate transparency logs are a top passive source of subdomains.

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