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Network Attacks Via DNS
The Internet
Posted by timothy on Sunday August 01, @07:54AM
from the operator-please dept.
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."

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Also by timothy
Network Attacks Via DNS | Log in/Create an Account | Top | 147 comments | Search Discussion
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
TCP or UDP (Score:3, Interesting)
by rf0 (159958) <rghf@jvds.com> on Sunday August 01, @07:57AM (#9857143)
I have to wonder what protocol they used as DNS does allow for both UDP and TCP (TCP when the messages is over 512 bytes IIRC)

[ Reply to This ]
    Re:TCP or UDP (Score:5, Informative)
    by Anonymous Coward on Sunday August 01, @08:01AM (#9857157)
    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.
    [ Reply to This | Parent ]
      Re:TCP or UDP (Score:5, Interesting)
      by digitalhermit (113459) on Sunday August 01, @08:51AM (#9857254)

      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.

      Yup, and that's not the half of it. With the extensions being duct-taped onto the existing spec it makes it easier and easier to do this. I've seen some hacks to allow all sorts of arbitrary information to live on the servers, some relayed automatically because of the extensions, some used to modify how mail servers respond, some even for routing. It's nothing new (remember transferring data via ICMP ECHO?) but it's on a new level now.

      [ Reply to This | Parent ]
      • Re:TCP or UDP by AndroidCat (Score:1) Sunday August 01, @10:10AM
    • Re:TCP or UDP by Effugas (Score:2) Sunday August 01, @05:40PM
      Old news (Score:5, Informative)
      by fred87 (720738) <mail@nOSPAM.fredemmott.co.uk> on Sunday August 01, @07:58AM (#9857149)
      nessus has been pointing this out as a security hole in it's scan results for at least 3 months now...
      [ Reply to This ]
      • Re:Old news by fred87 (Score:3) Sunday August 01, @08:08AM
        • Re:Old news by Anonymous Coward (Score:3) Sunday August 01, @08:59AM
          • Re:Old news by Xoder (Score:2) Sunday August 01, @11:32AM
            • Re:Old news by strobert (Score:2) Sunday August 01, @05:59PM
              • 1 reply beneath your current threshold.
            • Re:Old news by Xaria (Score:1) Monday August 02, @12:50AM
              • 1 reply beneath your current threshold.
            • Re:Old news by thogard (Score:1) Sunday August 01, @10:14AM
              • Re:Old news by davidu (Score:2) Sunday August 01, @01:09PM
                • Re:Old news by lysander (Score:3) Sunday August 01, @02:03PM
                  • 1 reply beneath your current threshold.
              • Re:Old news by Effugas (Score:3) Sunday August 01, @05:29PM
                • Re:Old news by burns210 (Score:2) Sunday August 01, @05:37PM
                  • Re:Old news by jnull (Score:1) Monday August 02, @01:03PM
                    • 1 reply beneath your current threshold.
                    This is supposed to be 'news'? (Score:5, Informative)
                    by fw3 (523647) * on Sunday August 01, @08:01AM (#9857155)
                    (http://slashdot.org/ | Last Journal: Sunday December 21, @01:10PM)
                    Layering services over dns has been a discussed topic in books / seminars for at least a decade already.
                    [ Reply to This ]
                      Repeated (Score:2)
                      by lachlan76 (770870) <lachlan76@hotmaiGINSBERGl.com minus poet> on Sunday August 01, @08:02AM (#9857158)
                      This story seems quite similar to a previous one about using DNS for communications, from LayerOne. Incredibly stupid to use for mainstream communications, but perfect for hackers, with low data requirements, anyway.
                      [ Reply to This ]
                      • Re:Repeated by hesaigo999ca (Score:1) Sunday August 01, @05:54PM
                        So does this mean (Score:4, Funny)
                        by foidulus (743482) * on Sunday August 01, @08:03AM (#9857160)
                        That is should change my bookmark to [] now?
                        [ Reply to This ]
                          In other news... (Score:3, Funny)
                          by Zorilla (791636) on Sunday August 01, @08:04AM (#9857162)
                          ...Microsoft plans to release a security update to Windows XP which will secure the DNS hack. For all future internet usage, please enter in It's not a bug, it's a feature.
                          [ Reply to This ]
                            90% of the internet is valnerable ... (Score:4, Interesting)
                            by after (669640) on Sunday August 01, @08:04AM (#9857163)
                            (http://nan2d.com/ | Last Journal: Thursday October 16, @11:51PM)
                            to somthing called DNS poison [google.com]. Why? Because system administrators are anal and fail to realize that software like BIND is not written to be secure. Hell, DNS was not even designed for such a large internet. The original DNS implementors were bad programmers and designers.

                            BIND9... don't get your hopes up. The BIND company sells paches for their software. Meaning that if you don't pay them money then you're going to be running an errornouse DNS server.

                            Still most people use BIND for two reasons: no one wants to learn the crusty details of DNS and 2) Linux comes with BIND as it's default name library.

                            Alternative like djbdns [cr.yp.to] should be used.
                            [ Reply to This ]
                            helpful (Score:5, Funny)
                            by Scythr0x0rs (801943) * on Sunday August 01, @08:12AM (#9857177)
                            some good people could break into the nameservers of a large ISP such as AOL and send out spoofed NS records for update.windowsupdate.com or whatever it is and deploy linux to all windows users.

                            Warning: this update may require a reboot.
                            [ Reply to This ]
                            • Re:helpful by Scythr0x0rs (Score:1) Sunday August 01, @12:42PM
                              • 1 reply beneath your current threshold.
                              This is why.... (Score:3, Insightful)
                              by Cylix (55374) on Sunday August 01, @08:25AM (#9857196)
                              (http://www.bastardism.com/cylix | Last Journal: Thursday March 07, @12:05PM)
                              I've set control lists for DNS for a long long time.

                              After the IP over DNS tunnel came out... it was actually a bit necessary. Our staff would do anything to get out of doing work...
                              [ Reply to This ]
                              Suspicious? (Score:3, Insightful)
                              by timgoh0 (781057) on Sunday August 01, @08:37AM (#9857218)
                              Wouldn't large amounts of DNS traffic look suspicious? Especially if they originated from one machine.
                              [ Reply to This ]
                              • Re:Suspicious? by Anonymous Coward (Score:2) Sunday August 01, @09:12AM
                                • Re:Suspicious? by Anonymous Coward (Score:1) Sunday August 01, @05:50PM
                                  • 1 reply beneath your current threshold.
                                • Re:Suspicious? by Shadowlore (Score:2) Sunday August 01, @09:52PM
                                  • 2 replies beneath your current threshold.
                                  Cheating Wireless networks (Score:5, Insightful)
                                  by technothrasher (689062) on Sunday August 01, @08:40AM (#9857225)
                                  I've noticed in the past that many of the public wireless networks that want you to pay to use allow DNS traffic to flow even before you've paid. I've often thought that'd you could use that to build a tunnel and not have to pay for service.

                                  Mind you, I've never done it because it would be kind of rotten, but it did cross my mind.

                                  [ Reply to This ]
                                  Reason why (Score:1)
                                  by Teppich (769850) on Sunday August 01, @09:01AM (#9857274)
                                  (Last Journal: Monday August 02, @04:31PM)
                                  my standard iptables rules only allow some ISPs dns-servers.
                                  [ Reply to This ]
                                  Misleading Title (Score:1, Informative)
                                  by Anonymous Coward on Sunday August 01, @09:06AM (#9857285)
                                  The title of the post is misleading. DNS can't be actually used to attack a network, only to slip sensitive data by firewalls.
                                  [ Reply to This ]
                                    Harmless? (Score:5, Insightful)
                                    by jjeffrey (558890) <james@jgj.org.uk> on Sunday August 01, @09:12AM (#9857294)
                                    I don't think that networks allow DNS because it is harmless, but because it is necessary, that's an important distinction.
                                    [ Reply to This ]
                                      So? (Score:1)
                                      by jbb999 (758019) on Sunday August 01, @09:13AM (#9857297)
                                      If you can send data in any form you can tunnel anything you like over it. Why is this news?
                                      [ Reply to This ]
                                      • Re:So? by AndroidCat (Score:1) Sunday August 01, @10:19AM
                                        Well known that DNS is iffy,s urely? (Score:1, Redundant)
                                        by mwillems (266506) on Sunday August 01, @09:32AM (#9857379)
                                        Surely we all know that "DNS" comes at the top of the list of the Internet's vulnerabilities? Tunneling data; many bugs in DNS software over the years; vulnerability to DOS: Surely we all know this already - why is this news?

                                        DNS was an afterthought - but it seems to me a very necessary one, and one we will have to continue to live with.

                                        [ Reply to This ]
                                          That's why you use proxies! (Score:5, Informative)
                                          by wowbagger (69688) on Sunday August 01, @09:38AM (#9857396)
                                          (http://slashdot.org/~wowbagger/journal/ | Last Journal: Friday April 30, @10:12AM)
                                          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.
                                          [ Reply to This ]
                                          Covert communication over DNS tunnels (Score:2, Insightful)
                                          by Timbo (75953) on Sunday August 01, @09:41AM (#9857402)
                                          There was an old slashdot story [slashdot.org] eons ago about people using DNS tunnels to abuse the free dial up lines used for setting up a dial up ISP account. Covert comms over DNS is nothing new, but oddly it doesn't seem to have ever caught on.
                                          [ Reply to This ]
                                            Firewall 1 lets through DNS by default ? (Score:2)
                                            by rainer_d (115765) on Sunday August 01, @10:29AM (#9857582)

                                            I've read somewhere that there are some "implicit" rules in the Firewall 1 default configuration that let DNS through anyway.
                                            Is that true ? I have the eval CD here, but haven't had the time and the resources to test it.

                                            [ Reply to This ]
                                            Duh... (Score:5, Funny)
                                            by blixel (158224) on Sunday August 01, @10:34AM (#9857607)
                                            That flaw in most firms' network security leaves a vulnerability that can be used by hackers to sneak intellectual property outside a company, communicate with a compromised server inside the company,

                                            In other security news alerts, there was a major hole disocvered in SSH. It turns out if a hacker installs a rogue SSH daemon on the server, he can do nefarious things with it.
                                            [ Reply to This ]
                                              Re:Duh... (Score:4, Informative)
                                              by Effugas (2378) on Sunday August 01, @05:36PM (#9859558)
                                              Most trojans need to poll the outside world periodically, to determine whether they have a new set of operations to execute. With this approach, no polling is necessary -- there's an open pipe _into_ the organization, and the trojan can remain perfectly silent.

                                              [ Reply to This | Parent ]
                                              "without DNS" = LDAP (Score:4, Interesting)
                                              by Anonymous Coward on Sunday August 01, @10:56AM (#9857709)
                                              Note that LDAP is fully capable of doing host name resolution, there's even an RFC for it (AFAIK the one that specifies how to store POSIX user info also specifies how to store host names).
                                              And in fact, DNS can be used for user details via Hesiod.

                                              Both LDAP and DNS are hierarchical federated database systems. Personally, I find current LDAP implementations to be more manageable, better designed, and generally nicer (can set very fine grained permissions) than current DNS implementations. A name system based on LDAP rather than DNS would be fully feasible and IMHO as or more globally scalable.

                                              But we must distinguish between DNS-the-protocol and DNS-the-implementations - It would be possible to have the same piece of software answer both DNS and LDAP queries from the same database. Hey, hello Microsoft Active Directory! But MAD is nasty for other reasons - so where are the Open Source projects to provide a slapd plugin for DNS protocol lookup to openldap databases? It should actually be pretty simple, maybe it's so simple no-one is interested hacking on it....

                                              [ Reply to This ]
                                              How about this : OpenVPN over UDP port 53 ie. DNS (Score:5, Interesting)
                                              by anti-NAT (709310) on Sunday August 01, @11:02AM (#9857747)

                                              Thought of this almost two years ago. Run OpenVPN [sourceforge.net] over UDP port 53. I figure a fair number of firewalls may not analyse UDP DNS traffic to see if it actually is UDP DNS traffic. Haven't had a chance to try it out though.

                                              Thinking big picture, you realise that once opportunistic IPsec becomes available, and with IPv6 it will be, any device in the network trying to interpret traffic, such as firewalls and proxy servers, will become just about useless.

                                              [ Reply to This ]
                                                nstx (Score:2)
                                                by cosmol (143886) on Sunday August 01, @11:26AM (#9857834)
                                                I saw this story through google news and I thought, "better check slashdot." Got an article from 2000.

                                                http://slashdot.org/article.pl?sid=00/09/10/223024 2&tid=95 [slashdot.org]

                                                and the current version of nstx:http://nstx.dereference.de/nstx/nstx-1.1-beta 5.tgz [dereference.de]

                                                [ Reply to This ]
                                                • Re:nstx by nutznboltz (Score:3) Sunday August 01, @05:56PM
                                                  Quick Summary: What's New (Score:4, Informative)
                                                  by Effugas (2378) on Sunday August 01, @05:16PM (#9859470)
                                                  OK, let me repeat.

                                                  Throwing arbitrary data in DNS -- NOT a big deal.

                                                  Even doing network tunneling over DNS -- ALSO not that big a deal; NSTX has been doing this for a while.

                                                  DNS radio is new. By segmenting audio into small chunks, we actually get universal caching of the streaming signal -- a functionality we've never really had before. Generally, audio broadcast over the Internet falls apart after a few thousand users. Based on this ring-buffer-into-BIND architecture, combined with the utterly minimal bandwidth load of Speex, we should be able to host audio for a much greater number of listeners.

                                                  The entire suite of incoming attacks to firewalls are also new. DNS trusts the hierarchy to tell it the next hop to its target name; since I can acquire second level domains in the hierarchy for minimal cost, it's trivial for me to insert arbitrary destinations along the DNS route path. In technical terms, whenever a recursing resolver comes to my name server to resolve a name, rather than providing an answer, I can redirect that request to another, supposedly authoritative server. That server can be at any address -- even one I cannot IP route to -- but if the resolver communicating with me can route to that address (say my communication will reach that host. If there's an SSH over DNS daemon running on, I've now achieved incoming connectivity to the network of my choice, completely bypassing firewalls and a trojan's need to poll.

                                                  Recursion on dual hosted interfaces is not even necessary. There are large numbers of applications that, upon receiving untrusted traffic, execute DNS name lookups. Most commonly, they are reverse PTR lookups, but occasionally there are other types (MX from mail servers, most notably) that can be easily induced. When they are induced, the hierarchy is followed. When the hierarchy is followed, the attacks previously discussed start working. In practice, this means an IDS triggers the DNS server to start proxying traffic between an external attacker host and an internal trojaned machine. Nasty.

                                                  There's some other stuff -- check out the slides and the code -- but long story short, there's some new stuff out :-)

                                                  [ Reply to This ]
                                                    Advertisements and Spam (Score:2)
                                                    by HermanAB (661181) on Sunday August 01, @05:27PM (#9859523)
                                                    are more of a problem than covert channels. Every cell phone is a covert channel out of a business. Since DNS can't be used to deliver advertisements, I don't see a business threat here. It may be a concern to a military installation though.
                                                    [ Reply to This ]
                                                    • 9 replies beneath your current threshold.
                                                    • HAIR TONICS, please!!
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