What is subdomain enumeration? 🧠
Every company has a main domain — but often dozens or hundreds of subdomains linked to internal teams, external tools, or past projects. Think:
staging.yourcompany.com
dev-api.yourcompany.com
legacy-dashboard.yourcompany.com
Subdomain enumeration is the process of discovering these subdomains to understand what’s publicly exposed — often without the company realizing it.
Why it’s risky 💣
Subdomains are rarely treated with the same security rigor as production systems. Many are:
created ad hoc by dev or marketing teams
tied to tools that no one actively maintains
forgotten after a project ends
still resolving to live infrastructure
These forgotten assets often lack:
strong authentication
regular updates
access control
visibility by the security team
And yet: they’re publicly resolvable. Meaning anyone — including attackers — can find them in seconds.
How attackers (and tools) discover them
Subdomain enumeration requires no credentials, no access, and no phishing. Just smart scanning.
Here’s how they do it:
DNS brute-forcing with known prefixes like admin., test., portal.
Certificate transparency logs that publicly list subdomains from issued SSL certs
Public DNS databases and passive DNS feeds
Search engine operators like site: or inurl: queries
APIs and OSINT tools that combine all the above
✅ How to stay ahead of it
You don’t need to out-hack attackers — you just need to see what they see.
Here’s what we recommend:
Continuously monitor your DNS and subdomain footprint
Remove or lock down dev/test environments when they’re no longer in use
Use wildcard certificates cautiously
Treat every internet-facing service as if it will be discovered — because it will
Automate discovery with tools that fit your workflow (like Tresal)
👀 See your subdomains — before attackers do
Tresal continuously maps your external attack surface, including forgotten subdomains and misconfigured services.
No agents. No setup. No sales call.
Just visibility.