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/
When a CA issues an SSL/TLS certificate, they’re required to submit it to public CT logs (append-only, cryptographically verifiable ledgers). This was designed to detect misissued or malicious certificates.
Red and Blue team alike use this resource (crt.sh) to enumerate subdomains.
You need to look at the DNS server used by whatever client is resolving that name. If it’s going to an external recursive resolver instead of using your own internal DNS server then you could be leaking lookups to the wider internet.
My guess would be NSEC zone walking if your DNS provider supports DNSSEC. But that shouldn’t work with unregistered or wildcard domains
The next guess would be during setup, someone somewhere got ahold of your SNI (and/or outgoing DNS requests). Maybe your ISP/VPN service actually logs them and announce it to the world
I suggest next time, try setting up without any over-the-internet traffic at all. E.g. always use
curlwith the--resolveflag on the same VM as Apache to check if it’s workingChrome: Sees new website domain
Google: 👀
Crawlers typically crawl by ip.
Are u sure they just not using ip?
U need to expressly configure drop connection if invalid domain.
I use similar pattern and have 0 crawls.
Is this at a webserver level?
If you have browser with search suggestions enabled, everything you type in URL bar gets sent to a search engine like Google to give you URL suggestions. I would not be surprised if Google uses this data to check what it knows about the domain you entered, and if it sees that it doesn’t know anything, it sends the bot to scan it to get more information.
But in general, you can’t access a domain without using a browser which might send that what you type to some company’s backend and voila, you leaked your data.
Easily verified by creating another bunch of domains and using a browser that doesn’t do tracking - like waterfox
What you can do is segregate networks.
If the browser runs in, say, a VM with only access to the intranet and no internet access at all, this risk is greatly reduced.
Maybe using subfinder?
Maybe that particular subdomain is getting treated as the default virtual host by Apache? Are the other subdomains receiving scans too?
I don’t use Apache much, but NGINX sometimes surprises on what it uses if the default is not specifically defined.
A long time ago, I turned a PC in my basement into a web server. No DNS. Just a static IP address. Within 15 minutes, the logs showed it was getting scanned.
SSL encrypts traffic in-transit. You need to set up auth/access control. Even better, stick it behind a Web Application Firewall.
Or set up a tunnel. Cloudflare offers a free one: https://developers.cloudflare.com/cloudflare-one/networks/connectors/cloudflare-tunnel/
if you use Let’s Encrypt (ACME protocol) AFAIK you can find all domains registered in a directory that even has a search, no matter if it’s wildcard or not.
It was something like this https://crt.sh/ but can’t find the site exactly anymore
LE: you can also find some here https://search.censys.io/
Holy shit… I thought it was DNS resolver selling these data
deleted by creator
This.
That’s why temping obscurity for security is not a good idea. Doesn’t take much to be “safe”, at least reasonably safe. But that not much its good practice to be done :)
No. Not this.
Op is doing hidden subdomain pattern. Wildcard dns and wildcard ssl.
This way subdomain acts as a password and application essentially inaccessible for bot crawls.
Works very well
Apparently it doesn’t.
minimal setup is still required 🤷
Holy shit, this has every cert I’ve ever generated or renewed since 2015.
Certificate Transparency makes public all issued certificates in the form of a distributed ledger, giving website owners and auditors the ability to detect and expose inappropriately issued certificates.
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I’ve seen in this thread:
Fewer Letters More Letters CA (SSL) Certificate Authority DNS Domain Name Service/System IP Internet Protocol SSL Secure Sockets Layer, for transparent encryption TLS Transport Layer Security, supersedes SSL VPN Virtual Private Network VPS Virtual Private Server (opposed to shared hosting)
7 acronyms in this thread; the most compressed thread commented on today has 16 acronyms.
[Thread #990 for this comm, first seen 11th Jan 2026, 01:25] [FAQ] [Full list] [Contact] [Source code]
Good bot
Kudos to the bot.
For anyone who needs to read it: At the end of the day this is obscurity, not security; however obscurity is a good secondary defense because it buys time.
I too would be interested to learn how this leaked
Isnt security mostly achieved by heavy obscurity? A password secures because other people dont know what it is, it is obscured.
They’re not the same.
Hiding an unlocked treasure chest in the forest is obscurity. Sure, you might be the only one who knows it’s there at first but eventually someone might come across it.
Having a vault at a bank branch is security - everyone knows there’s a vault there, but you’ll be damned if you’re going to get into it when you’re not authorized.
Good passwords, when implemented correctly, use hashing (one way encryption) to provide security. It’s not obscured, people know you need a password to access the thing (in our example)
In cryptography, there’s a difference between “secrets” (like passwords and encryption keys), and hiding / obscuring something (like steganography or changing your web server to run on a different port)
it’s not even obscurity; it’s logged publicly.
It’s not. Wildcard DNS and wildcard cert. Domain is not logged publicly.
People that keep saying logged publicly simply don’t understand setup and technology
How is it being logged publicly? Like OP said there is no specific subdomain registered in the DNS records (instead using a wildcard). Same for the SSL cert. Only things I can think of is the browser leaking the subdomains (through google or Microsoft) or the DNS queries themselves being logged and leaked. (Possibly by the ISP inspecting the traffic or logging and leaking on their own DNS servers?). I would hardly call either of those public.
Do post again if you figure it out!
Will do!
Reverse DNS? Or vuln scans just hitting IPs. Don’t need DNS for that.
Op is doing hidden subdomain pattern. Wildcard dns and wildcard ssl.
This way subdomain acts as a password and application essentially inaccessible for bot crawls.
Works very well
