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Ask HN: How did the internet discover my subdomain?

287 points govideo | 3 comments | 06 Mar 25 22:34 UTC | HN request time: 0.644s | source

I have a domain that is not live. As expected, loading the domain returns: Error 1016.

However...I have a subdomain with a not obvious name, like: userfileupload.sampledomain.com

This subdomain IS LIVE but has NOT been publicized/posted anywhere. It's a custom URL for authenticated users to upload media with presigned url to my Cloudflare r2 bucket.

I am using CloudFlare for my DNS.

How did the internet find my subdomain? Some sample user agents are: "Expanse, a Palo Alto Networks company, searches across the global IPv4 space multiple times per day to identify customers' presences on the Internet. If you would like to be excluded from our scans, please send IP addresses/domains to: scaninfo@paloaltonetworks.com", "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_7; en-us) AppleWebKit/534.20.8 (KHTML, like Gecko) Version/5.1 Safari/534.20.8", "Mozilla/5.0 (Linux; Android 9; Redmi Note 5 Pro) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.89 Mobile Safari/537.36",

The bots are GET requests which are failing, as designed, but I'm wondering how the bots even knew the subdomain existed?!

Show context
CGamesPlay ◴[07 Mar 25 13:41 UTC] No.43290059[source]▶
Be careful with these. I had a subdomain like this (completely unlisted) with a Google OAuth flow on it, using a development mode Google app. Somehow, the domain was discovered, and Google decided that using their OAuth flow was a phishing scam, and delisted my entire toplevel domain as a result!
replies(1): >>43290142 #
1. yoavm ◴[07 Mar 25 13:51 UTC] No.43290142[source]▶
What do you mean "careful with these"? With subdomains?
replies(1): >>43290154 #
2. CGamesPlay ◴[07 Mar 25 13:53 UTC] No.43290154[source]▶
Yes, unlisted subdomains. I updated my post to be clearer.
replies(1): >>43290215 #
3. joshstrange ◴[07 Mar 25 14:02 UTC] No.43290215[source]▶
I must be missing something. What does “unlisted” mean in this context?

I have plenty of subdomains I don’t “advertise” (tell people about online) but “unlisted” is a weird thing to call those. Also I don’t see how it would matter at all when it comes to Google auth.

My guess is they blocked it based on the subdomain name itself. I made a “steamgames” subdomain to list stream games I have extra copies of (from bundles) for friends to grab for free. Less than a day after I put it up I started getting chrome scare pages. I switched it to “games” and there have been no issues.