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Network Attacks Via DNS
Iphtashu Fitz writes "Without DNS the internet wouldn't be all that useful. Despite being a ubiquitous part of the internet it is overlooked by many as a potential security hole. At this weekends Defcon 12 conference in Las Vegas, security researcher Dan Kaminsky warned that DNS can open up seemingly secure networks to attack. Because most firewalls and other security devices treat DNS requests as harmless it provides an excellent conduit for transferring covert data in and out of otherwise protected systems. At Defcon, Kaminsky demonstrated some software that allows a server to act as a communications hub using DNS. This let him transmit instant messages and even audio streams over an encrypted connection carried by spoofed DNS requests."
"Because the data looked like typical DNS traffic it wouldn't be detected or logged by firewalls or intrusion detection systems. He also pointed out that monitoring DNS could help in other unrelated ways: because the recent MSBlast worm did lookups on windowsupdate.com infected machines could have been detected by simply monitoring DNS server logs."
nessus has been pointing this out as a security hole in it's scan results for at least 3 months now...
Layering services over dns has been a discussed topic in books / seminars for at least a decade already.
Linux is Linux, if One need clarify their dist: <Dist>/GNU Linux
bsds are of course just BSD
An interesting property of DNS is that there are servers all over the net which will happily relay your message. Even if your only connection to the net is through application level proxies, you probably have a local DNS resolver. That's all you need. No packet has to traverse the firewall directly.
They may have used spoofed DNS packets just to bypass a firewall, but information can also be tunneled in real DNS packets, so even if you only allow DNS to/from certain servers, you're still not safe from this leak.
>ufortunately, djbdns is not open-source.
Incorrect, it is open source.
It isn't GPL.
There's a big difference.
>Until a true open source alternative to BIND appears, we're stuck with it.
By "true alternative" do you mean it has to be GPLable?
Get real. djbdns' source is 100% available for you to look at and patch to your hearts content. If you find an error, send a fix to DJB and he'll add it after review. He'll even give you $500 as a reward for your hard work. Find me a GPL program that makes an offer like that.
Now, if he doesn't like your patch, you can post the patch on the internet. You can even put it alongside the source. You can even make an autopatch program that will patch djbdns during make so that dumb users can handle the process
For the disbelievers, here's the source code.
Here's bernstein's statement about the freedom of his software. Feel free to print it out and sign it if you're insane on the idea he can revoke your license.
If you could be told what you can see or read, then it follows that you could be told what to say or think - BoC
That is why any GOOD sysadmin will set up the system so that there is a single DNS server for the plant, and that server and that server alone is allowed to send and receive DNS packets to the greater Internet - all other machines are to use the local DNS server.
Not only does this GREATLY reduce the amount of DNS traffic a shop produces (by caching all requests locally) it helps prevent this sort of foolishness by requiring all packets to be well formed DNS packets - else the server drops them.
Then, you can block any client that makes more than a few requests a second.
Yes, it is easier to set up a firewall to be very porous to outbound traffic, but it is more secure to deny all direct access, and force clients to run through proxies for the various services.
www.eFax.com are spammers