full-disclosure - DNS Smurf revisited

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Date: Fri May 27 15:28:45 2005
From: ian-fulldisclosure at penguinhosting.net (Ian Gulliver)
Subject: DNS Smurf revisited

DNS smurf is old news:

http://www.s0ftpj.org/docs/spj-002-000.txt
http://www.ciac.org/ciac/bulletins/j-063.shtml

However, as ISPs continue to operate networks that let spoofed packets
out this issue deserves a little publicity again.

10:17:07.641061 IP (tos 0x0, ttl  64, id 46429, offset 0, flags [DF], length: 49) XXXXXXXXXXXXX.44295 > c.gtld-servers.net.domain: [udp sum ok]  18297 ANY? org. (21)
10:17:07.673800 IP (tos 0x0, ttl  43, id 0, offset 0, flags [DF], length: 468) c.gtld-servers.net.domain > XXXXXXXXXXXXX.44295: 18297- 0/13/13 (440)

% echo "2 k 468 49 / p" | dc
9.55

That's a 9.5X amplification of outgoing traffic; you can probably break
10X with a little more work on the query and nameserver choices.


SOLUTIONS
---------

ISPs: Drop outgoing packets that don't originate from within your
network.  You should already be doing this, as it stops a variety of
other attacks.

NS operators: Ratelimit?


Attached is a modernized proof of concept.

-- 
Ian Gulliver
Penguin Hosting
"Failure is not an option; it comes bundled with your Microsoft products."
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