Learning objectives

• Explain Subdomain Discovery in plain language
• Connect the idea to everyday systems (shops, banks, college portals) without attacking them
• Know what “in scope / out of scope” means for this topic
• Complete the knowledge check and recall the ethical boundary

1. In one sentence

Find hostnames like api., dev., staging. that expand attack surface — only for in-scope roots.

2. Why it matters (daily life)

dev.shop.com often weaker than www. Companies forget old subdomains (classic takeover class of bugs).

3. How it works

Certificate transparency, DNS brute (authorized), search engines, ASN mapping — then verify resolution.

4. Real-world / authorized lab example

Forgotten jira.company.com still live → authorized web test target if in scope.

5. Defender’s view

If you are blue team or a developer: assume an authorized tester (or an attacker) will apply this technique. Reduce exposure, monitor loudly for active recon, and fix findings with clear owners and due dates.

6. Common mistakes

Brute-forcing huge wordlists against production without rate limits/approval.

7. Practical habit (authorized systems only)

1. Confirm written permission and IP/domain scope.
2. Practice the idea on CYNARKS Labs / intentionally vulnerable VMs.
3. Keep a dated note: what you tried, what you saw, what you recommend.
4. Never “verify” on Instagram, PhonePe, college portals, or random internet hosts.

8. Memory tip

Explain this step to a friend in one minute using a college portal or small-shop website story — without attacking anything real.

Knowledge Check

Q1. Why are staging subdomains risky?

A. Follow written scope, document findings, and report responsibly
B. Attack any live public site “for practice” without permission
C. Skip notes and only keep screenshots on a personal phone
D. Publish full exploit details before the client can patch

Q2. Name one discovery source.?

A. Follow written scope, document findings, and report responsibly
B. Attack any live public site “for practice” without permission
C. Skip notes and only keep screenshots on a personal phone
D. Publish full exploit details before the client can patch

Q3. What do you verify after a name is found?

A. Follow written scope, document findings, and report responsibly
B. Attack any live public site “for practice” without permission
C. Skip notes and only keep screenshots on a personal phone
D. Publish full exploit details before the client can patch

Answer Key

1. A
2. A
3. A

Lesson Summary

Subdomain Discovery sits inside a professional pentest workflow: permission → careful technique → evidence → fix. Skill without authorization is not “practice” — it is risk.

Coming next

Continue the Ethical Hacking path in syllabus order. Stay in scope.

CYNARKS Academy – Learn to Understand. Practice to Defend.
Practice only in CYNARKS Labs or systems with written authorization.