Associated Domains Discovery - ProjectDiscovery Documentation

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Modern enterprises frequently have complex infrastructures spread across many domains and business units. ProjectDiscovery’s Associated Domains Discovery gives security teams instant visibility into their entire organizational attack surface by automatically discovering related domains through multiple intelligence sources. The platform correlates data from three primary sources:

Acquisition History - Corporate subsidiaries and acquired companies from business intelligence sources
Certificate History - SSL/TLS certificate transparency logs revealing shared infrastructure
WHOIS History - Domain registration records identifying common ownership

This multi-source approach ensures comprehensive coverage, discovering domains that might be missed when relying on a single data source.

Why Associated Domains Discovery Matters

Tracking assets across multiple organizations, subsidiaries, and technical infrastructures is notoriously difficult when done manually. Security teams traditionally had to compile lists of related domains from internal knowledge or public records, then run separate scans for each-a time-consuming and error-prone process.

Common Challenges

Incomplete Visibility: Large organizations might have dozens of related domains across subsidiaries, product brands, and acquired companies. Manually mapping all these entities is a huge challenge. In practice, many enterprises have hundreds or even thousands of related entities, making it difficult to get a clear picture of their full attack surface.
Constant Change: Mergers, acquisitions, and infrastructure changes mean the set of assets is constantly evolving. Without continuous updates, asset inventories become outdated quickly. Domains can change ownership or get spun up rapidly in cloud environments.
Fragmented Data Sources: Information about related domains is scattered across financial databases, certificate logs, WHOIS records, and press releases. Mapping out which domains are owned by your organization requires extensive research across multiple sources.
Risk of Unknown Assets: Unknown or unmanaged assets can lead to security incidents. A forgotten website under an acquired company or a domain sharing your SSL certificate could become an easy target for attackers.

Discovery Sources

Associated Domains Discovery leverages three distinct intelligence sources, each providing unique insights into domain relationships.

Acquisition History

Source: Business Intelligence & Corporate Records ProjectDiscovery integrates with corporate intelligence sources to automatically identify subsidiaries, acquired companies, and related brands associated with your organization. What it discovers:

Subsidiary companies and their domains
Acquired company assets
Related brands and product domains
Corporate hierarchy relationships

Evidence provided:

Field	Description
`acquired_company`	Name of the acquired company
`acquired_date`	Date of acquisition
`acquirer_name`	Parent organization name
`source_url`	Link to source information

When you onboard to the platform, it automatically pulls known subsidiaries and related entities-giving you an instant snapshot of your organization’s broad footprint without manual research.

Certificate History

Source: Certificate Transparency Logs SSL/TLS certificates often reveal domain relationships that aren’t visible through other means. Organizations frequently use shared certificates across related properties, or certificate organization fields expose ownership. What it discovers:

Domains sharing the same SSL certificate
Domains with matching certificate organization names
Wildcard certificate coverage
Certificate authority patterns

Evidence provided:

Field	Description
`cert_common_name`	Certificate common name (CN)
`cert_org_name`	Organization name in certificate
`cert_issuer`	Certificate authority
`cert_serial`	Certificate serial number
`cert_issued_date`	When certificate was issued
`cert_expiry_date`	Certificate expiration date

WHOIS History

Source: Domain Registration Records WHOIS records provide authoritative information about domain ownership. By analyzing registration patterns, the platform identifies domains that share organizational ownership. What it discovers:

Domains with matching registrant organizations
Shared registrar patterns
Common registration dates (bulk registrations)
Related WHOIS contact information

Evidence provided:

Field	Description
`registrant_org`	Registrant organization name
`registrar`	Domain registrar
`registration_date`	Domain registration date
`expiry_date`	Domain expiration date
`whois_server`	WHOIS server used
`orgname`	WHOIS organization name

Using Associated Domains Discovery

Via the Platform UI

Access Associated Domains in the platform to view domains related to your verified domains. By default, the platform automatically discovers and displays associated domains for all your verified domains.

Navigate to Assets → Domains in the left sidebar
View associated domains automatically discovered for your verified domains
Optionally search for a specific domain to explore its associations
Review results grouped by discovery source
Add discovered domains to your asset inventory for monitoring

Via the API

Query associated domains programmatically using the Associated Domains API. Default behavior - Returns associated domains for all your verified domains:

curl -X GET "https://api.projectdiscovery.io/v1/domain/associated" \
  -H "X-Api-Key: YOUR_API_KEY"

Query specific domain - Optionally specify a domain to get its associated domains:

curl -X GET "https://api.projectdiscovery.io/v1/domain/associated?domain=meta.com" \
  -H "X-Api-Key: YOUR_API_KEY"

Filter by source:

# Only acquisition history
curl -X GET "https://api.projectdiscovery.io/v1/domain/associated?domain=meta.com&source=acquisition_history" \
  -H "X-Api-Key: YOUR_API_KEY"

# Only certificate history
curl -X GET "https://api.projectdiscovery.io/v1/domain/associated?domain=meta.com&source=certificate_history" \
  -H "X-Api-Key: YOUR_API_KEY"

# Multiple sources
curl -X GET "https://api.projectdiscovery.io/v1/domain/associated?domain=meta.com&source=certificate_history,whois_history" \
  -H "X-Api-Key: YOUR_API_KEY"

Filter by liveness:

# Only active/reachable domains
curl -X GET "https://api.projectdiscovery.io/v1/domain/associated?domain=meta.com&active=true" \
  -H "X-Api-Key: YOUR_API_KEY"

Pagination and sorting:

# Paginated results sorted by subdomain count
curl -X GET "https://api.projectdiscovery.io/v1/domain/associated?domain=meta.com&limit=50&page=1&sort=subdomain_count" \
  -H "X-Api-Key: YOUR_API_KEY"

Raw output (plain text):

# Get just domain names, one per line
curl -X GET "https://api.projectdiscovery.io/v1/domain/associated?domain=meta.com&raw=true" \
  -H "X-Api-Key: YOUR_API_KEY"

Associated Domains Discovery returns up to 10 results per query on standard plans. Upgrade to Enterprise for complete associated domain discovery results.

Response Structure

The API returns comprehensive information about each discovered domain:

{
  "domain": "meta.com",
  "sources": ["acquisition_history", "certificate_history", "whois_history"],
  "sources_count": {
    "acquisition_history": 5,
    "certificate_history": 12,
    "whois_history": 8
  },
  "unique_count": 18,
  "results": [
    {
      "domain": "subsidiary.com",
      "sources": ["acquisition_history"],
      "evidence": {
        "acquired_company": "Subsidiary Inc",
        "acquired_date": "2023-06-15",
        "acquirer_name": "Meta",
        "active": true,
        "subdomain_count": 45,
        "status_code": 200,
        "title": "Subsidiary Inc - Homepage"
      }
    },
    {
      "domain": "example-cdn.com",
      "sources": ["certificate_history"],
      "evidence": {
        "cert_common_name": "*.meta.com",
        "cert_org_name": "Meta Platforms, Inc.",
        "cert_issuer": "DigiCert Inc",
        "cert_issued_date": "2024-01-15",
        "cert_expiry_date": "2025-01-15",
        "active": true,
        "subdomain_count": 3
      }
    },
    {
      "domain": "example-backup.com",
      "sources": ["whois_history"],
      "evidence": {
        "registrant_org": "Meta Platforms, Inc.",
        "registrar": "GoDaddy",
        "registration_date": "2020-03-10",
        "expiry_date": "2025-03-10",
        "active": false
      }
    }
  ]
}

Key Response Fields

Field	Description
`domain`	The queried domain
`sources`	List of all sources used in the query
`sources_count`	Number of results from each source
`unique_count`	Total unique associated domains found
`results`	Array of discovered domains with evidence

Per-Result Fields

Field	Description
`domain`	The associated domain name
`sources`	Which sources identified this domain
`evidence`	Source-specific proof of association
`evidence.active`	Whether the domain is currently reachable
`evidence.subdomain_count`	Number of known subdomains
`evidence.status_code`	HTTP status code (if probed)
`evidence.title`	HTTP page title (if available)

Best Practices

Maximize Discovery Coverage

Use all sources: Don’t filter by source initially-let the platform correlate across all three sources for maximum coverage.
Check inactive domains: Domains marked as active: false may still be valuable-they could be parked domains or temporarily down services that attackers might target.
Review subdomain counts: High subdomain counts often indicate active infrastructure worth investigating further.

Integrate into Your Workflow

Automate discovery: Use the API to periodically query associated domains and automatically add new discoveries to your asset inventory.
Set up alerts: Configure notifications when new associated domains are discovered to stay ahead of your expanding attack surface.
Cross-reference with scans: Run vulnerability scans on newly discovered domains to identify exposure before attackers do.

Handle Multi-Organization Environments

Start with your primary domain: Query your main corporate domain first to establish the baseline.
Iterate on discoveries: Query significant discovered domains to find second-degree associations.
Validate ownership: Before adding domains to your scanning scope, verify ownership to avoid scanning third-party infrastructure.

Continuous Enrichment

Associated Domains Discovery is not a one-time static pull. The platform continuously enhances its correlation capabilities:

Real-time certificate monitoring: New certificates are indexed as they appear in transparency logs
WHOIS update tracking: Registration changes are detected and reflected in results
Acquisition intelligence: Corporate events are tracked and correlated with domain ownership
Liveness probing: Domain reachability is regularly checked and updated

As your organization grows-launching new websites, spinning up cloud services, or acquiring companies-the platform automatically updates discoveries and keeps track of new potential entry points.

API Reference

For complete API documentation including all parameters, response schemas, and code examples in multiple languages, see the Associated Domains API Reference.

Cloud Platform

Documentation Index

​Why Associated Domains Discovery Matters

​Common Challenges

​Discovery Sources

​Acquisition History

​Certificate History

​WHOIS History

​Using Associated Domains Discovery

​Via the Platform UI

​Via the API

​Response Structure

​Key Response Fields

​Per-Result Fields

​Best Practices

​Maximize Discovery Coverage

​Integrate into Your Workflow

​Handle Multi-Organization Environments

​Continuous Enrichment

​API Reference

Why Associated Domains Discovery Matters

Common Challenges

Discovery Sources

Acquisition History

Certificate History

WHOIS History

Using Associated Domains Discovery

Via the Platform UI

Via the API

Response Structure

Key Response Fields

Per-Result Fields

Best Practices

Maximize Discovery Coverage

Integrate into Your Workflow

Handle Multi-Organization Environments

Continuous Enrichment

API Reference