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/
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, this has every cert I’ve ever generated or renewed since 2015.
Holy shit… I thought it was DNS resolver selling these data
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
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.
But this still doesn’t explain it. Like OP I also use a wildcard cert. The subdomains are never exposed.
TIL
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/
We’re always watching.
I believe that some DNS servers are configured to allow zone transfers without any kind of authentication. While properly configured servers will whitelist the IPs of secondaries they trust, for those that don’t, hackers can simply request a zone transfer and get all subdomains at once.
I don’t have any subdomains registered with DNS.
I attempted
dig axfr example.com @ns1.example.comreturned zone transfer DENIED
Yeah, this is interesting, I’ll dig more into this direction.
But the randomly generated subdomain has never seen a DNS registrar.
I do have *.mydomain.com registered though…hmmm
Did you yourself make a request to it or just set it up and not check it? My horrifying guess it that if you use SNI in a request every server in the middle could read the subdomain and some system in the internet routing is untrustworthy.
Previous experiments, yes, I sent a request. The random one, no.
If you do a GET / request against the IP (typically http too) does it yield a redirect to your proper fqdn? It shouldn’t return anything and remain stealthy as you likely dont want to expose anything directly on IP connections and rely solely on your vhosts.
Reverse DNS? Or vuln scans just hitting IPs. Don’t need DNS for that.
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.
Do you use an external DNS when accessing your subdomain? I can only guess that it’s the DNS leaking it.
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.
