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/
I run my webservers behind a pfsense firewall with ssl offloading(using a wildcard cert) with a static IP and use Haproxy to have sub-domain’s go to individual servers. Even though I’ve seen my fair share of scans, I only ever expose port 443 and keep things updated.
Recently though someone on here mentioned routing everything over Tailscale via a VPS. I didn’t want to pay for a VPS and frankly can’t even find one that is reasonably priced in the US(bandwidth limits mainly), so I threw Tailscale onto my pfsense, setup split-dns on Tailscale’s admin panel with my domain name, and then reconfigured Haproxy to listen on my Tailscale interface. Even got IPv6 working(huge pain due to a bug it seems). Oh and setup pfblocker.
My current plan is I’m going to run my webservers behind Tailscale and keep my game servers public and probably segment those servers to a different vlan/subnet/dmz/whatever. And maybe just have a www/blog landing page that is read only on 443 and have it’s config/admin panel accessible via my tailscale only.
Anyway, back on topic. I run my game servers and I don’t advertise them out anywhere(wildcard cert) and do whitelist only, yet I still see my minecraft servers get hit constantly on port 25565.
So not much you can do except minimize exposure as much as possible.
Do post again if you figure it out!
Will do!
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.
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.
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.
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?
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
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 workingAll the obvious things have been mentioned.
The only way to identify the problem is to share the exact steps youve followed and then others can reproduce.
Based on what youve told us, no one knows how the subdomain is leaked. Without meaning to be derisive, that suggests that something youve told us isn’t quite correct.
Well, the good news is that I at least think I’m doing all the right things.
I’ll spin up a new VM tomorrow and start from scratch.
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.
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.
TIL
But this still doesn’t explain it. Like OP I also use a wildcard cert. The subdomains are never exposed.
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/
Inb4 some lucky dude just ran sublist3r or wfuzz on your subdomain and got a hit
I mean, it could be… I’ll try it with a 128 char base 52 name and see what happens
Have you also tried making a subdomain and not making any requests to it yourself? So no browser access or other DNS resolution requests for the new subdomain. That should rule out some of the other possible causes suggested in the other comments.
Dang, it could be the upstream DNS server passing along client queries. Maybe the ISP?
In that case not even curl would be safe unless you could ensure all queries only resolve on your gear. Either use a host file entry or local DNS server.
Chrome: Sees new website domain
Google: 👀
Are you sure they’re hitting the hostname and not just the IP directly?
Shows up by name in the apache other_hosts…log, so yes
Going to IP directly could redirect to your first domain. This would trigger another request to your domain and could result in your logs.
You need to make sure to 444 drop connection immediately if wrong domain. Redirect to https should be configured after - I suspect ur config redirects
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/
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
Hmm. I feel like conflating a subdomain with a password is a particularly sketchy idea, but you do you.
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.
Holy shit… I thought it was DNS resolver selling these data
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