nanog mailing list archives
Re: DNS Amplification attack?
From: "Crist Clark" <Crist.Clark () globalstar com>
Date: Wed, 21 Jan 2009 11:23:47 -0800
On 1/20/2009 at 7:23 PM, Mark Andrews <Mark_Andrews () isc org> wrote:
In message <20090121140825.xwdzd4p64kgwo4go () web1 nswh com au>, jay () miscreant or g writes:On Tue, Jan 20, 2009 at 9:16 PM, Kameron Gasso <kgasso-lists () 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.
Another BIND-specific question since we're on the topic. I see some of our authorative servers being hit with these spoofs, and yes, the 9.3.5-P1 (that's what Sun supports in Solaris these days) were sending back answers from the cache... but wait... what cache? The view the Internet gets only has our authorative zones. There is no declaration for the root zone, master, slave, or hints. How does BIND have the root cached in that view? Where did it get it from? I guess it's hard coded somewhere? Blocking this in the firewall. 1:0 amplification better than the BIND fix, 1:1. But I'll get to the BIND fix anyway.
Current thread:
- Re: DNS Amplification attack?, (continued)
- Re: DNS Amplification attack? Kameron Gasso (Jan 20)
- Re: DNS Amplification attack? Christopher Morrow (Jan 20)
- Re: DNS Amplification attack? Kameron Gasso (Jan 20)
- Re: DNS Amplification attack? Christopher Morrow (Jan 20)
- Re: DNS Amplification attack? Chris Adams (Jan 20)
- Re: DNS Amplification attack? Stuart Henderson (Jan 21)
- Re: DNS Amplification attack? Christopher Morrow (Jan 20)
- Re: DNS Amplification attack? Kameron Gasso (Jan 20)
- Re: DNS Amplification attack? jay (Jan 20)
- Re: DNS Amplification attack? Chris Adams (Jan 20)
- Re: DNS Amplification attack? jay (Jan 20)
- Re: DNS Amplification attack? Mark Andrews (Jan 20)
- Re: DNS Amplification attack? Crist Clark (Jan 21)
- Re: DNS Amplification attack? Chris Adams (Jan 21)
- Re: DNS Amplification attack? Mark Andrews (Jan 21)
- Re: DNS Amplification attack? Paul Vixie (Jan 21)
- Re: DNS Amplification attack? Florian Weimer (Jan 22)
- Re: DNS Amplification attack? Chris Adams (Jan 20)