Guide
Dangling CNAME — possible subdomain takeover
How StackSiren Deep Scan detects this issue and how to fix it. Severity typically high.
Why it matters
Dangling CNAME — possible subdomain takeover is a common finding on vibe-coded and AI-built apps that ship client bundles, shared backends or platform defaults without a security pass.
StackSiren reports this from read-only checks (GET, HEAD or OPTIONS only). It does not exploit the issue.
How to fix it
Remove the orphaned DNS CNAME, or claim the resource at the target host (Vercel/Netlify/GitHub/Heroku/Azure) so nobody else can. Audit unused preview and staging records regularly.
How StackSiren Deep Scan checks
Deep Scan runs only on hosts you have verified you own (DNS TXT or /.well-known file) and consented to test. Findings include a short evidence string; secret values are masked.
See the Acceptable Use Policy and Active scanning terms for what Deep Scan is and is not.