I should clarify I wasn’t a upper level sys admin managing those servers, I just used them or maintained accounts being a rank and file technician
While I get the fundamental concept of DNS as a phonebook for your IPs. I am not sure why it is joked around if something goes haywire or someone breaks something.
Is it because if you get no DNS, people can’t log in through their AD accounts, browse the Internet?
Afaik DNS is a bit of a rabbit hole topic, maybe that’s why people joke about it due to DNS being this “No one really knows how this magic name matching box works”?
Please correct me, I’d genuinely like to know why this is prevalent from you guys.
I never would have thought of it but I recently saw a novel use of DNS to exfiltrate data from a compromised server.
My employer takes security very seriously. Our public facing web servers are very thoroughly locked down, or so we thought. We contract with companies like HackerOne to perform penetration testing etc. One of their white hat hackers managed a remote command attack, and copied data off of the server via a string of DNS queries.
Suppose the hacker owned the domain example.com, and he had his own authoritative nameserver for it. He just ran a series of commands that took, for example, a password file, and ran DNS queries for line1.example.com, line2.example.com, line3.example.com and so on for each line in the file. As a result the log file on his DNS server collected each line of the password file as it responded to each query.
I’m trying to digest this
You’re saying he was stealing data from the target server by appending it line-by-line to dns requests sent to his nameserver? Wouldn’t he have needed to both be on the target server and already have access to the data?
Our web servers are locked down in such a way that you can’t copy data off of them using standard protocols like scp, ftp, and even http, etc. Our firewall blocks all such outbound traffic.
This hacker found a bug in a framework used on our web servers that let him execute commands remotely. When commands to copy data off the server failed using those more typical methods he switched to a more novel (and difficult) method of leveraging DNS instead. He discovered we weren’t locking DNS down the same way we were locking other protocols down and used that as a way to extract data from our server.
Ah, ok, that makes sense! So there was a separate bug in the framework that granted him limited remote access, but because the server had tight control over outbound connections he had to use a novel way of getting the data back out
Basically: He crawled in through the sewer and then robbed the bank one stack of bills at a time via pigeon courier.
Yes, but it’s not necessarily as simple as having full ssh access or something like that. Plus getting data out by DNS queries is probably much harder to detect than something like sftp or http posts.
Could be used to exfiltrate data when you only can make commands, but not see their output. There might be other and easier exfiltration possibilities then, but this is a creative solution that uses a very common protocol and will probably be available on any machine.