DNS Amplification attack?

Mark Andrews Mark_Andrews at isc.org
Wed Jan 21 03:23:32 UTC 2009

In message <20090121140825.xwdzd4p64kgwo4go at web1.nswh.com.au>, jay at miscreant.or
g writes:
> > On Tue, Jan 20, 2009 at 9:16 PM, Kameron Gasso <kgasso-lists at visp.net> wro=
> te:
> > We're also seeing a great number of these, but the idiots spoofing the
> > queries are hitting several non-recursive nameservers we host - and only
> > generating 59-byte "REFUSED" replies.
> >
> > Looks like they probably just grabbed a bunch of DNS hosts out of WHOIS
> > and hoped that they were recursive resolvers.
> First post to this list, play nice :)
> Are you sure about this? I'm seeing these requests on /every/ =20
> (unrelated) NS I have access to, which numbers several dozen, in =20
> various countries across the world, and from various registries (.net, =20
> .org, .com.au). The spread of servers I've checked is so random that =20
> I'm wondering just how many NS records they've laid their hands on.
> I've also noticed that on a server running BIND 9.3.4-P1 with =20
> recursion disabled, they're still appear to be getting the list of =20
> root NS's from cache, which is a 272-byte response to a 61-byte =20
> request, which by my definition is an amplification.

	BIND 9.3.4-P1 is past end-of-life.

	You need to properly set allow-query at both the option/view
	level and at the zone level to prevent retrieving answers
	from the cache in 9.3.x.

		option/view level "allow-query { trusted; };"
		zone level "allow-query { any; };"

	BIND 9.4.x and later have allow-query-cache make the
	configuration job easier.  It also defaults to directly
	connected networks.

> Cheers,
> Jay
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org

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