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How are people discovering random subdomains on my server? (lemmy.blahaj.zone)

submitted 5 months ago* (last edited 5 months ago) by BonkTheAnnoyed@lemmy.blahaj.zone to c/selfhosted@lemmy.world

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I generated 16 character (upper/lower) subdomain and set up a virtual host for it in Apache, and within an hour was seeing vulnerability scans.

How are folks digging this up? What's the strategy to avoid this?

I am serving it all with a single wildcard SSL cert, if that's relevant.

Thanks

Edit:

I am using a single wildcard cert, with no subdomains attached/embedded/however those work
I don’t have any subdomains registered with DNS.
I attempted dig axfr example.com @ns1.example.com returned zone transfer DENIED

Edit 2: I'm left wondering, is there an apache endpoint that returns all configured virtual hosts?

Edit 3: I'm going to go through this hardening guide and try against with a new random subdomain https://www.tecmint.com/apache-security-tips/

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[–] toebert@piefed.social 4 points 5 months ago

I can't say I know the answer but a few ideas:

did you access it with a browser? Maybe it snitches on you or some extension does?
did you try to resolve it with a public DNS server at any point (are you sure nothing forwarded the request to one)?

You could try it again, create the domain in the config and then do absolutely nothing. Don't try to confirm it works in any way. If you don't see the same behaviour you can do one of the above and then the other and see when it kicks in. If it gets picked up without you doing anything..then pass!