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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: 0s | 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
thedougd ◴[07 Mar 25 05:23 UTC] No.43287552[source]▶
Some CAs (Amazon) allow not publishing to the Certificate Transparency Log. But if you do this, browsers will block the connection by default. Chromium browsers have a policy option to skip this check for selected URLs. See: CertificateTransparencyEnforcementDisabledForURLs.

Some may find this more desirable than wildcard certificates and their drawbacks.

replies(3): >>43287622 #>>43287653 #>>43287677 #
klntsky ◴[07 Mar 25 05:45 UTC] No.43287622[source]▶
> Some may find this more desirable

Why?

replies(1): >>43289854 #
1. thedougd ◴[07 Mar 25 13:07 UTC] No.43289854[source]▶
A CISA article on wildcard security risks. Some of this is in part from common misimplementations (e.g.reusing private keys across servers), but not all of it.

https://www.cisa.gov/news-events/alerts/2021/10/08/nsa-relea... Direct: https://media.defense.gov/2021/Oct/07/2002869955/-1/-1/0/CSI...