Safeguarding Against Subdomain Takeovers – A Comprehensive Checklist

Subdomain Takeovers Techhyme

Subdomain takeovers pose a significant threat to the security of web applications, potentially leading to unauthorized access and exploitation of external services. This comprehensive checklist outlines proactive steps to identify and mitigate subdomain takeover risks, ensuring the integrity and security of your domain infrastructure.

1. Enumerate Subdomains

Use specialized tools such as Sublist3r, Amass, or dnsrecon to enumerate subdomains associated with your main domain. This step provides a comprehensive view of your domain landscape, aiding in subsequent analysis.

2. Analyze DNS Records

Check DNS records, including CNAME, A, AAAA, and MX records, for subdomains pointing to external services or expired domains. This analysis helps identify potential vulnerabilities related to subdomain configurations.

3. Check HTTP Responses

Examine HTTP responses for error messages or status codes that may indicate an unclaimed or expired external service. Unexpected responses may reveal opportunities for subdomain takeover.

4. Use Online Services

Utilize online services such as or Censys to gather subdomain and certificate data for your main domain. This external data can provide additional insights into subdomains associated with your domain.

5. Test Common Third-Party Services

Check if subdomains are pointing to common third-party services susceptible to subdomain takeover attacks, such as AWS S3, GitHub Pages, or Heroku. Misconfigurations in these services can lead to security risks.

6. Test for Dangling CNAME Records

Look for dangling CNAME records that point to external services that have been deleted or expired. Orphaned records represent potential opportunities for subdomain takeover.

7. Monitor Domain Registration

Monitor domain registration information for expired domains that can be taken over. Expired domains may still have active DNS records pointing to external services, creating a subdomain takeover risk.

8. Use Subdomain Takeover Tools

Employ specialized tools like SubOver, Subjack, or tko-subs to automatically identify subdomain takeover vulnerabilities. These tools streamline the identification process and provide insights into potential risks.

9. Check for Misconfigured DNS Settings

Examine DNS settings for misconfigurations that might lead to subdomain takeover vulnerabilities. Ensure that DNS configurations are accurate and secure.

10. Test for Wildcard DNS Records

Check for wildcard DNS records that might expose subdomains to takeover attacks. Wildcard configurations can inadvertently allow unauthorized access to subdomains.

11. Check for Abandoned Subdomains

Look for abandoned subdomains that still point to unused external services. These subdomains, if overlooked, can become potential targets for takeover attacks.

12. Test for Improper Redirects

Check if subdomains are improperly redirecting traffic to external services that can be taken over. Improper redirects may create opportunities for subdomain takeover.

13. Monitor Domain Ownership Changes

Monitor domain ownership changes for potential takeover opportunities. Changes in ownership may impact the security posture of your domain, highlighting potential risks.

14. Collaborate with Third-Party Service Providers

Work collaboratively with third-party service providers to ensure proper domain configuration and prevent subdomain takeover. Regular communication helps address potential misconfigurations.

15. Regularly Audit Subdomain Configurations

Periodically review your subdomain configurations to identify and mitigate potential subdomain takeover risks. Regular audits contribute to ongoing security assessments and ensure the continued integrity of your domain infrastructure.


By diligently following this comprehensive checklist, organizations can significantly reduce the risk of subdomain takeovers and fortify their web application security. Regular monitoring, collaboration with third-party providers, and ongoing assessments of subdomain configurations are essential components of a proactive security strategy.

Incorporating these practices into your security protocols helps create a robust defense against potential subdomain takeover threats.

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