Subdomain Takeover

Table of Contents

• Option 1: Remove Dangling CNAME
• Option 2: Update CNAME

Option 1: Remove Dangling CNAME

1. If the subdomain is no longer in use, then from your DNS zone, remove the subdomain’s DNS record.
2. Review application code and configuration for references to subdomains no longer in use and remove those references.

Option 2: Update the CNAME

1. If the subdomain is still in use, update the subdomain’s DNS record so that its CNAME(s) point to valid resources.

References

• Subdomain Takeovers: Thoughts on Risk
• Prevent Dangling DNS Entries and Avoid Subdomain Takeover