DNS DoS Attack

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Looks like one of my name servers (CentOS 5) gets a lot of malicious queries. The cpu load is constantly about 3 %. I put on stricter limits on who is allowed recursive queries, but this does not affect the CPU
load. I also updated bind.

I temporarily turned on querylog (command: rndc querylog), and noticed that I get over 200 queries like this per second:

Are there any ways to mitigate this, or do I just have to wait?

– Jussi

6 thoughts on - DNS DoS Attack

  • meh, if its coming from lots of random hosts, then fail2ban style techniques won’t work. I assume this is an authoritative name server?
    does it have recursive queries disabled so it can only return results for the domain(s) its authoritative for ?

  • Am Thu, 16 Aug 2012 22:18:19 -0700
    schrieb John R Pierce :

    It’s a common “attack”.

    Just search google. I think, someone mentioned a firewall rule here a couple of weeks ago to block these types of queries.

  • Yes, it is authoritative. Recursive queries were open very widely. That may be why I started to get plenty of requests. But I think that 240 per second is not normal anymore, it must me malicious.

    I believe my name server was used as a mediator only, and the real target (through recursive queries) was some other public nameserver.

    This morning I restricted recursive queries to trusted networks only. The load dropped slowly to 20 % of what it was before.

    – Jussi

  • Interesting idea. In that case the ip’s in my logs would point to the targets of the attact. I checked a few of them, and they look more like hijacked victims, or ns query mediators like me. I don’t see a common factor.

    …icon.com (Ricoh, Japanese office machines)
    …unum.com (employee insurances, I think)
    sexy-lingerie.uk.com mnet04-40.austin.datafoundry.com
    …netmagicians.com ns1.p10.dynect.net http://www.macsales.com
    66-226-73-103.dedicated.codero.net ns.rackspace.com ns1.clt.peak-10.com (their webpage: “We’re rock solid”!)

    – Jussi

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