Fingerprint Web Server (Passive)

Test Objectives

Find the version and type of a running web server to determine known
vulnerabilities and the appropriate exploits to use during testing.
(OWASP Testing Guide v4.0 – Fingerprint Web Server OTG-INFO-002)

Passive:

Collect information without direct interaction with your target website.

Online Tools:

Netcraft Site Report: http://toolbar.netcraft.com/site_report
Builtwith: http://builtwith.com/
Shodan Search

References: