What it looks like
A subdomain on your domain has a CNAME record pointing at a surge.sh target, and loading that subdomain returns Surge's unclaimed page rather than a working site. The visible signature is a page containing text along the lines of "project not found".
Both signals are needed. A CNAME pointing at Surge 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
Surge projects are trivially created and claimed, which makes an abandoned record here easy to capture.
What an attacker gets
- Content served from your subdomain, on your domain, usually with a valid certificate that Surge 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. Surge is commonly used for quick demos, so these records are usually left from a one-off that nobody remembers.
The full removal steps for any provider are in the dangling record guide.
Stopping the next one
These appear whenever a hosted service is trialled and dropped, so a single 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 of them is on anyone's mind.