DNS Attacks

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1

Hi list,

I am wondering if anyone else has seen a large amount of DNS queries
coming from various IP ranges in China. I have been trying to find a
pattern in the attacks but so far I have come up blank. I am completly
guessing these are possibly DNS amplification attacks but I am not
sure. Usually what I see is this:

- Attacks most commonly between the hours of 4AM-4PM UTC
- DNS queries appear to be for real domains that the DNS servers in
question are authoritive for (I can't really see any pattern there,
there are about 150,000 zones on the servers in question)
- From a range of IP's there will be an attack for approximately 5-10
minutes before stopping and then a break of 30 minutes or so before
another attack from a different IP range
- Every IP range has been from China

I have limited the number of queries that can be done to mitigate this
but its messing up my pretty netflow graphs due to the spikes in
flows/packets being sent.

Does anyone have any ideas what the reasoning behind this could be? I
would also be interested to hear from anyone else experiencing this
too.

I can provide IP ranges from where I am seeing the issue but it does
vary a lot between the attacks with the only pattern every time being
the source address is located in China. I read a thread earlier,
http://seclists.org/nanog/2011/Nov/920, which sounds like the exact
thing I am seeing.

Thanks

2

Most of the time you will be being used as a amplifier and the
source traffic is spoofed. The short periods are so that it is
harder to trace the compromised machines.

Mark

3

Hi list,

I am wondering if anyone else has seen a large amount of DNS queries
coming from various IP ranges in China. I have been trying to find a

china is a big country....

pattern in the attacks but so far I have come up blank. I am completly
guessing these are possibly DNS amplification attacks but I am not
sure. Usually what I see is this:

- Attacks most commonly between the hours of 4AM-4PM UTC
- DNS queries appear to be for real domains that the DNS servers in
question are authoritive for (I can't really see any pattern there,
there are about 150,000 zones on the servers in question)

yup

- From a range of IP's there will be an attack for approximately 5-10
minutes before stopping and then a break of 30 minutes or so before
another attack from a different IP range

marka noted that the source is really the thing being attacked, that
seems to be the case in the incidents I've seen (and which I"ve seen
other folks also make note of, over the last ~2-3 months)

- Every IP range has been from China

yup, probably over .cn peer links? if you have them...

I have limited the number of queries that can be done to mitigate this
but its messing up my pretty netflow graphs due to the spikes in
flows/packets being sent.

yea... you can't really limit queries, unless you can react in almost
real-time to drop the queries on the floor before your servers see
them :frowning: or capacity-plan for the spikes, which is... rough.

Does anyone have any ideas what the reasoning behind this could be? I
would also be interested to hear from anyone else experiencing this
too.

lots of folks are chattering privately about this, it's something in
china attacking chinese users.The BW and PPS rates involved are likely
quite high...

I can provide IP ranges from where I am seeing the issue but it does
vary a lot between the attacks with the only pattern every time being
the source address is located in China. I read a thread earlier,
nanog: Recent DNS attacks from China?, which sounds like the exact
thing I am seeing.

it probably is... if you run decently large auth complexes with lots
of domains, welcome to the party.

-chris

4

At various seemingly random times over the past week I have had a DNS which is behind a firewall come under attack. The firewall is significant because the attacks killed the firewall as it is rather under specified (not my idea..).

It did originate from Chinese address space and consisted of DNS queries for lots of hosts. There was also a port-scan in the traffic and a SYN attack on a few hosts on the same small subnet as the DNS, a web server and an open SSH port.

5

DNS servers (nor any other kind of server, for that matter) should never be placed behind stateful firewalls - the largest firewall one can build or buy will choke under even moderate DDoS attacks due to state-table exhaustion:

<https://files.me.com/roland.dobbins/679xji>

6

Hi list,

I am wondering if anyone else has seen a large amount of DNS
queries coming from various IP ranges in China. I have been trying
to find a pattern in the attacks but so far I have come up blank. I
am completly guessing these are possibly DNS amplification attacks
but I am not sure. Usually what I see is this:

At various seemingly random times over the past week I have had a DNS
which is behind a firewall come under attack. The firewall is
significant because the attacks killed the firewall as it is rather
under specified (not my idea..).

Given the the pps rate and the cps rate of DNS requests are rather
similar one expects the value of inspecting unsolicited queries to your
nameserver to be rather low.

7

Hi -

We've been victims of these attacks many a times and more recently
towards our customer dns servers which was rated at ~ 4gbps for a
duration of 30mins.

Tracking the source of an attack is simplified when the source is more
likely to be "valid".

The nature of these attacks for us was a combination of amplification
and spoofed, however implementing anti-spoofing (uRFP) specially bcp38
is a good idea not saying its a fix but certainly the attack methodology
will significantly lessen.

As Matt Katz put it rightly so, "Distributed denial of service can only
be solved with distributed delivery of service".

regards,
/virendra

8

We ran into a 25Gbps SNMP 'reply/amplification attack' from a cable modem network about a month ago.

Hopefully the particular network has fixed that issue now, but it was a banner day to be sure.

Thanks,
-Drew

9

We are seeing this too, though we don't have the kind of exposure some of the larger providers do. fwiw.. If for some reason, you can't use a dedicated box for DNS and/or a simple acl to protect services on a box, you can turn off connection tracking in iptables per-port using the NOTRACK target.

iptables -t raw -I PREROUTING -p udp --dport 53 -j NOTRACK
iptables -t raw -I OUTPUT -p udp --sport 53 -j NOTRACK

http://www.frozentux.net/iptables-tutorial/iptables-tutorial.html#NOTRACKTARGET

Ken

10

http://thehackernews.com/2012/02/fbi-will-shutdown-internet-on-march-8.html