OSINT & Defense
Understanding why subdomain, port, and infrastructure data is publicly available — and how it's used for defense, not offense.
The Reality of Public Internet Data
Every device connected to the internet broadcasts information simply by existing. This isn't a flaw — it's how the internet works. When you host a website, run a mail server, or operate any internet-facing service, certain information becomes publicly visible:
Subdomains
DNS records are public by design. Certificate Transparency logs record every SSL certificate issued.
Open Ports
Services must listen on ports to accept connections. Port visibility is inherent to TCP/IP.
CPE Data
Service banners and headers often reveal software versions for compatibility purposes.
Industry Leaders in Internet Scanning
Major technology companies continuously scan the internet and make this data available. This isn't controversial — it's a recognized industry practice that improves security for everyone:
Shodan
shodan.io
The world's first search engine for Internet-connected devices. Scans the entire IPv4 address space, indexing banners, ports, and services.
Censys
censys.io
Founded by researchers from the University of Michigan. Provides continuous monitoring of internet-wide scan data and attack surface management.
RiskIQ / Microsoft
Acquired by Microsoft
Enterprise attack surface management platform. Now part of Microsoft Defender for Threat Intelligence.
BinaryEdge
binaryedge.io
Collects and analyzes data from internet-wide scans, providing threat intelligence and attack surface visibility.
ZoomEye
zoomeye.org
Chinese cyberspace search engine that maps and monitors global internet infrastructure and connected devices.
crt.sh
Certificate Transparency
Database of all SSL/TLS certificates from Certificate Transparency logs. A key source for subdomain discovery.
We Do NOT Perform Active Scanning
SubDomains Finder does not scan any targets.
We aggregate publicly available data from the sources mentioned above. When you search for a domain on our platform:
- We query our cached database of publicly available information
- No packets are sent to the target domain
- No active reconnaissance or port scanning occurs
- Your search is completely passive and leaves no trace on the target
OSINT for Defense
Understanding your own attack surface is the first step to defending it. Organizations use OSINT tools like ours to:
🔍 Asset Discovery
Find forgotten subdomains, development servers, or shadow IT assets that might be exposed.
⚠️ Vulnerability Assessment
Identify outdated software versions or misconfigurations visible from the internet.
📊 Continuous Monitoring
Track changes to your infrastructure as seen from an external perspective.
🛡️ Threat Intelligence
Understand what attackers can see before they use it against you.
“Know thyself, know thy enemy. A thousand battles, a thousand victories.”— Sun Tzu, The Art of War
In cybersecurity, knowing what attackers can see about your organization is the first step to defense.