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Ask HN: How did the internet discover my subdomain?

287 points govideo | 1 comments | 06 Mar 25 22:34 UTC | HN request time: 0.21s | 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?!

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arkfil ◴[07 Mar 25 07:21 UTC] No.43287929[source]▶
paloAlto (network devices like firewalls etc) is able to scan the sites that users want to visit behind their devices. these are very popular devices in many companies. users can also have agents installed on their computers that also have access to the sites they visit.
replies(1): >>43288265 #
1. opello ◴[07 Mar 25 08:28 UTC] No.43288265[source]▶
This is what I was thinking it must be, along the lines of Cisco NAC. Could monitor via browser plugin for full URLs or DNS server for domains.

I imagine the certificate transparency log is the avenue, but local monitoring and reporting up as a new URL or domain to scan for malware seems similarly plausible.