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Comment by kstrauser | Hacker News Reader

Hey, it's me!

I'd added a new hostname to a long-existing domain. Then I added that hostname as a new virtual host to a Caddy server I've been running for a long time. The requests were to that vhost, i.e. using the `Host: my-new-host.example.com` header, not just running `curl http://1.2.3.4`. They were asking for the brand-new host by name.

After hashing it out with some friends on Mastodon, I think it's most likely because Caddy acquired a Let's Encrypt cert, those certs are logged[0], and attackers pounce on new hosts as soon as they're in the logs.

[0]https://letsencrypt.org/docs/ct-logs/

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Yes, this is a downside of certificate transparency. Also, using Let’s Encrypt certs for internal hosts, as some do for convenience, means you’re publishing your internal hostnames. Use an internal CA if that worries you.

If you care, you can use a wildcard cert. E.g. instead of getting a cert for foo.example.com, get one for *.foo.example.com, and then use an obscure subdomain. AFAIK, nobody is bruteforcing subdomains on wildcard certs.

They are

Are they brute forcing them, or are they relying on the fact that most users of wildcard certs also have wildcard DNS entries, so it's just that everything is actually available. Wildcard DNS pointing to a web server with a wildcard cert will pass through to the web server, and at that point the web server responds with a 404 if the host header isn't one configured for virtual hosts.

Didn't the wildcard cert still need the alt-names specifying the host for the browser to accept the certificate as fully valid? I remember being annoyed by warnings until I added them a decade ago while playing around with a private CA at a previous job

Yes, /cn is deprecated. But letsencrypt adds your wildcard into subjAltNames as well and it works great.

Great point. This was no big deal for me today. I was prepared for it. I mainly posted this to warn others: if you put a server online, it will be attacked, and it's going to be way sooner than you would have believed. You can't get away with, "yeah, I know I left some extra files laying around, but I'll clean them up and lock everything down as soon as I'm finished with the setup." Nope. That's not an option.

yup its lets encrypt. they publish the new certs to a list anyone can pull

all publicly trusted CAs (that want to work in browsers?) do this

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