Conducting External Reconnaissance with OSINT

When to Use

• Performing the initial reconnaissance phase of a penetration test to gather intelligence before active scanning
• Mapping an organization's external attack surface to identify unknown or shadow IT assets
• Collecting employee information, email formats, and organizational structure for social engineering campaigns
• Identifying exposed credentials, leaked data, or sensitive documents published on the internet
• Scoping the breadth of an organization's digital footprint prior to a red team engagement

Do not use for stalking, harassment, or unauthorized surveillance of individuals. OSINT gathering must be conducted within the scope of an authorized engagement and comply with applicable privacy laws (GDPR, CCPA).

Prerequisites

• Written authorization to perform reconnaissance against the target organization
• Dedicated research workstation with a VPN or Tor for anonymized queries when required
• OSINT framework tools installed: Amass, theHarvester, Shodan CLI, Recon-ng, SpiderFoot
• API keys for Shodan, Censys, SecurityTrails, Hunter.io, VirusTotal, and GitHub for enhanced results
• Disposable email accounts for accessing services that require registration during research

Workflow

Step 1: Domain and DNS Enumeration

Enumerate all domains, subdomains, and DNS records associated with the target:

• Root domain identification: Start with the primary domain and identify all related domains through reverse WHOIS lookups on registrant name, email, and organization using whoxy.com or domaintools.com
• Subdomain enumeration: Run multiple tools for comprehensive coverage:
  • amass enum -passive -d target.com -o amass_subs.txt for passive subdomain discovery from 40+ data sources
  • subfinder -d target.com -all -o subfinder_subs.txt for fast passive enumeration
  • crt.sh certificate transparency log queries: curl -s "https://crt.sh/?q=%25.target.com&output=json" | jq -r '.[].name_value' | sort -u
• DNS record analysis: Query for all record types: dig target.com ANY, check for SPF, DKIM, DMARC records that reveal email infrastructure, and enumerate MX records to identify email providers
• Zone transfer attempt: dig axfr @ns1.target.com target.com to check for misconfigured DNS servers
• Consolidate results: Merge, deduplicate, and resolve all discovered subdomains to IP addresses. Map IP addresses to ASN and hosting providers.

Step 2: Infrastructure and Service Discovery

Identify internet-facing infrastructure without directly scanning target systems:

• Shodan: shodan search "ssl.cert.subject.cn:target.com" to find all internet-facing services with TLS certificates for the target domain. Also search by organization name and IP ranges.
• Censys: Search for target's IP ranges and TLS certificates to identify services, technologies, and potential vulnerabilities indexed from internet-wide scanning
• Cloud asset discovery: Check for S3 buckets (target-com, target-backup, target-dev), Azure Blob storage (target.blob.core.windows.net), and GCP storage using tools like cloud_enum
• WAF and CDN identification: Use wafw00f target.com to identify web application firewalls and CDN providers that may mask the origin server IP
• Historical data: Use Wayback Machine (web.archive.org) to find removed pages, old application versions, and forgotten endpoints

Step 3: Email and Personnel Intelligence

Gather employee information and email addresses for social engineering preparation:

• Email harvesting: theHarvester -d target.com -b all -f harvest_results.html to collect emails from search engines, LinkedIn, and data sources
• Email format identification: Use hunter.io to determine the email format (first.last, flast, firstl) and verify deliverability
• LinkedIn reconnaissance: Identify employees by department, particularly IT administrators, security team members, and executives. Note technologies mentioned in job postings and employee profiles.
• Organizational chart: Build an org chart from LinkedIn data to understand reporting structures, identify key personnel, and map departments
• Social media analysis: Review employee social media profiles for information about internal tools, technologies, office locations, badge photos, and security practices

…