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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

85 comments fedilink hide all child comments

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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[–] kumi@feddit.online 12 points 5 months ago* (last edited 5 months ago) (1 children)

You say you have a wildcard cert but just to make sure: I don't suppose you've used ACME for Letsencrypt or some other publicly trusted CA to issue a cert including the affected name? If so it will be public in Certificate Transparency Logs.

If not I'd do it again and closely log and monitor every packet leaving the box.

[–] BonkTheAnnoyed@lemmy.blahaj.zone 13 points 5 months ago (1 children)

The random name is not in the public log. Someone else suggested that earlier. I checked CRT.sh and while my primary domain is there, the random one isn't.

[–] kumi@feddit.online 7 points 5 months ago* (last edited 5 months ago)

My next suspicion from what you've shared so far apart from what others suggested would be something out of the http server loop.

Have you used some free public DNS server and inadvertently queried it with the name from a container or something? Developer tooling building some app with analytics not disabled? Any locally connected AI agents having access to it?