←back to thread

Ask HN: How did the internet discover my subdomain?

287 points govideo | 2 comments | 06 Mar 25 22:34 UTC | HN request time: 0.573s | 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
yatralalala ◴[07 Mar 25 12:49 UTC] No.43289743[source]▶
Hi, our company does this basically "as-a-service".

The options how to find it are basically limitless. Best source is probably Certificate Transparency project as others suggested. But it does not end there, some other things that we do are things like internet crawl, domain bruteforcing on wildcard dns, dangling vhosts identification, default certs on servers (connect to IP on 443 and get default cert) and many others.

Security by obscurity does not work. You can not rely on "people won't find it". Once it's online, everyone can find it. No matter how you hide it.

replies(13): >>43289843 #>>43290143 #>>43290420 #>>43290596 #>>43290783 #>>43292505 #>>43292547 #>>43292687 #>>43293087 #>>43303762 #>>43309048 #>>43317788 #>>43341607 #
TZubiri ◴[07 Mar 25 13:06 UTC] No.43289843[source]▶
"Security by obscurity does not work"

This is one of those false voyeur OS internet tennets designed to get people to publish their stuff.

Obscurity is a fine strategy, if you don't post your source that's good. If you post your source, that's a risk.

The fact that you can't rely on that security measure is just a basic security tennet that applies to everything: don't rely on a single security measure, use redundant barriers.

Truth is we don't know how the subdomain got leaked. Subdomains can be passwords and a well crafted subdomain should not leak, if it leaks there is a reason.

replies(16): >>43290226 #>>43290237 #>>43290330 #>>43290608 #>>43290616 #>>43290675 #>>43290677 #>>43290740 #>>43290760 #>>43291317 #>>43291775 #>>43291815 #>>43292414 #>>43292523 #>>43292777 #>>43295244 #
1. bob1029 ◴[07 Mar 25 16:08 UTC] No.43291317[source]▶
Obscurity can be fantastic.

One of my favorite patterns for sending large files around is to drop them in a public blob storage bucket with a type 4 guid as the name. No consumer needs to authenticate or sign in. They just need to know the resource name. After a period of time the files can be automatically expired to minimize the impact of URL sharing/stealing.

replies(1): >>43298495 #
2. genewitch ◴[08 Mar 25 08:12 UTC] No.43298495[source]▶
Wouldn't the blob storage host be able to see your obscure file?

I suppose if it's encrypted, no. Like the pastebin service I run, it's encrypted at rest. It doesn't even touch disks, so I mean, that's a decent answer to mine own question.