What it looks like
A subdomain on your domain has a CNAME pointing at a vercel.app or vercel-dns target, and loading it returns Vercel's unclaimed page rather than a working site. The visible signature is text along the lines of "The deployment could not be found".
Both signals are needed. A CNAME pointing at Vercel is completely normal when the service is in use. It only matters when the target is no longer claimed.
Why it can be taken over
Removing a project or a domain from Vercel frees the association, and the domain can then be added to a different account's project.
What an attacker gets
- Content served from your subdomain, on your domain, usually with a valid certificate Vercel issues automatically.
- A phishing address that passes every check a cautious person would run, because it genuinely is your domain.
- Access to any cookie your main site scopes to the parent domain, which can include session data.
How to fix it
Remove the record. Vercel is used heavily for previews and staging, so these accumulate quickly on agency-managed domains.
Full removal steps for any DNS provider are in the dangling record guide.
Stopping the next one
These appear whenever a hosted service is trialled and dropped, so one cleanup does not settle it. The habit worth building is deleting the DNS record in the same sitting as the cancellation, because those are separate actions and only one is on anyone's mind.