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WHOIS Lookup
A protocol used to query databases that store the registered users or assignees of an internet resource.
PORT:
43
PROTOCOL:
TCP
FORMAT:
Text-based
What is WHOIS Lookup?
WHOIS is a public database that contains information about domain name ownership, including registrar name, registration dates, and sometimes contact info (though often redacted for privacy/GDPR).
How it Works
A WHOIS client connects to a WHOIS server (either the registry or registrar) on port 43 and submits a query for a domain. The server returns a structured text response.
Key Use Cases
Checking if a domain is available for registration.
Identifying the owner of a domain for legal or business inquiries.
Verifying the expiration date of a competitor or partner domain.
Advanced Details
With the introduction of GDPR, much of the personal information previously available in WHOIS is now hidden behind "Privacy Proxy" services or redacted entirely.
Cybersecurity Pros & Cons
Security Advantages
- WHOIS is the primary tool for attributing malicious domains to threat actors via registrant pattern analysis.
- Pivot analysis on registrant email/org fields can uncover entire campaigns of malicious domains from one actor.
- WHOIS data reveals nameservers, creation dates, and registrar — all essential for threat intelligence enrichment.
- Security researchers use WHOIS correlation to build connected-domain graphs linking phishing infrastructure.
Security Limitations
- GDPR and privacy proxy services have redacted most registrant data, severely limiting attribution capabilities.
- WHOIS data is self-reported with no verification — attackers freely use fake names and addresses.
- WHOIS port 43 transmits queries in cleartext, allowing ISPs to monitor which domains you are investigating.
- Rate limiting on WHOIS servers makes bulk investigative lookups slow and challenging for large-scale analysis.
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