To see how I actually solved this particular problem please see Thwarting the isc.org DDoS
It has long been held as best practice that one should use separate servers for authoritative (server) and recursive (client) domain name services. In some cases, this is not practical – for example I inherited one particular network at an ISP I do consulting for that has had its combined authoritative and recursive DNS servers on the same IP addresses for about a decade. Splitting up the roles of the servers would require either hundreds of clients with statically configured DNS to change their settings (imagine the load on tech support) or dozens of domain-holders to update their registrar glue, assuming their registrar even provides it (another load on tech support).
On this network I had – contrary to the gospel I know only too well – allowed recursive lookups from any source on the Internet for several years. I knew it was ideologically incorrect but have found it immeasurably handy to have a set of memorized nameserver IPs that you know will just work any time, anywhere in the world when you are tech supporting or trying to resolve an issue. No one seemed to notice for the years before and after I took on this client, and I couldn’t see the harm if a few folks started using them. It didn’t – and still doesn’t – make sense to me that a spammer would outsource their DNS operations to a vastly remote location (see updates at bottom, they are spammers but they’re actually trying to DDoS), at the cost of not only speed and latency but expensive bandwidth at all.
But today they did.
At around 12:40 I was notified of the situation and began my investigation. Handy-dandy iftop told me it was coming from one IP and they were making DNS requests – good news! The server wasn’t hacked – it was just being DoSed as a side-effect of over-querying. In fact, named was performing exceptionally well for a ~5-mbit/s load on a tiny virtual machine used to 150kbit/s, it was only the upstream bandwidth throttling that was keeping the flow in check.
I ran a full port scan on the attacker and much to my surprise it didn’t respond to pings and all ports were filtered. I was growing suspicious that this wasn’t a typical zombie. I blocked the attacker at the gateway and for a moment the network settled down. Then out of nowhere another attacker from a completely different IP showed up – I gave them a full scan and they too were filtered and unresponsive to ICMP echo requests. The new attacker came from 173.1.52.117.reverse.gogrid.com but forward lookups didn’t work. I didn’t have to go to their website to realize this was a VPS provider, clearly I was dealing with someone who owned their own kit – an organized spammer. My suspicions confirmed, I knew I would have to give up my little “public” DNS service and implement an Access Control List for recursive lookups.
By the time the third and most aggressive (getting pissed off about the IPs I was blocking?) wave of queries rolled around I had collected a list of all the networks and public addresses which require recursive lookups. Regardless of whether you have your authoritative services separated from your recursive unless your recursive server is on a private network it is best practice (and even then I would recommend it) to implement an ACL.
Open your named.conf and before the global options section, define an ACL as shown below. Notice that address ranges can be specified with CIDR notation:
acl "trusted" {
localhost;
192.168.0.0/16;
172.16.0.0/16;
10.0.0.0/8;
192.168.0.1;
222.222.222.222;
};
Now we can call the trusted ACL with the allow-recursive directive in the global options section. You can define any number of ACLs with different names, we’re just going with trusted as an example. Make sure the ACL includes every network and IP address that should have permission to perform recursive lookups – ensure your private subnets, public networks and any stray uplinks or remote locations are included. Those hosts not in the ACL and not performing lookups on domains for which your server is authoritative or already has cached will fail.
options {
version "fuck off, buddy";
recursion yes;
allow-recursion { trusted; };
};
Run rndc reload or restart BIND for the changes to take effect.
As you can tell from the bumps in my graph after the giant spike this guy (or these guys) is taking his time trying to figure out what I did, but the good news is he’s using less bandwidth and a whole whack of spam ain’t goin nowhere. Eventually they will realize that this server isn’t doing them any good and they’ll move on to greener pastures.
Finally, I got one of the attackers post-ACL to submit to a scan:
bzp ~ # nmap -P0 87.237.229.150
Starting Nmap 5.00 ( http://nmap.org ) at 2010-07-20 18:15 EDT
Interesting ports on 87.237.229.150:
Not shown: 990 closed ports
PORT STATE SERVICE
21/tcp open ftp
22/tcp open ssh
23/tcp open telnet
25/tcp filtered smtp
80/tcp open http
139/tcp filtered netbios-ssn
445/tcp filtered microsoft-ds
646/tcp filtered ldp
2000/tcp open callbook
8291/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 390.66 seconds
Well, that looks like any number of shared hosting servers, I wonder what’s on port 80:
Sweet, some sort of crazy European embedded linux routing solution. And their webconfig is wide open to cracking.
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If I had to guess I’d say this guy went the server route, or maybe he virtualizes his gateways like me. This distro has some neat stuff but it doesn’t have the balls and teeth of server-targeted ClearOS – and did they say free trial? I’ll have Nunuvut. This kind of explains why my port scans are being cut off though, a sufficiently advanced firewall like this probably has some sort of Intrusion Prevention mechanism and since I caught them with their web config (and telnet config for that matter) exposed and flapping in the breeze I’d say this is one of the installations my friend the spammer has not completed configuring, hence this one successful scan.
For the interest of Googlers trying to figure out why so and so is blasting the shit out of their name server(s) one IP at a time, here’s a list of IPs and PTRs (where available) I’ve caught so far:
82.225.94.140 sju13-2-82-225-94-140.fbx.proxad.net
173.1.52.117 173.1.52.117.reverse.gogrid.com
74.208.164.54 something from schlund.de
87.237.229.150 RIPE says the block belongs somewhere in Dubai 194.8.74.227 hosted by dragonara.net, listed as comment spammer by project honeypot
75.125.150.106 hosted by ev1servers.net
173.1.52.117 173.1.52.117.reverse.gogrid.com
98.126.124.203 MOLECHART.com
88.191.89.71
74.208.149.208 hosted by schlund.de
78.129.202.96
78.129.202.142
74.208.166.146 hosted by schlund.de
74.198.4.87 Rogers (Wave ???)
174.36.42.115 Italian-show-passion-quality-hostserver.com (lol)
98.126.54.227 98.126.54.227.STATIC.CUSTOMER.KRYPT.COM
74.198.0.53 Rogers (Wave ???)
88.191.109.130
85.25.150.72
173.192.224.100 173.192.224.100-static.reverse.softlayer.com
209.11.242.123 server12.elnastalk.com
Update I found 87.237.229.150 spamming on a strange Iraqi forum that reveals posters’ IP addresses to the general public. Strange indeed, but now I know I’m dealing with web form spammers, not e-mail spammers. Here’s a sample of the spam found at http://www.iraqal7ob.com/vb/t710.html
The image at the top was hotlinked from a free hosting service, the exact URL was http://hosting.bearzddl.com/uploads/9b0b60d466.jpg. Bearzddl is itself a shady file site and at the time of writing http://hosting.bearzddl.com/uploads/ provides a directory listing of all sorts of spammy looking images that have been uploaded through their free file hosting feature:
Update This morning we were attacked once again, I took the following sample capture:
11.695249 194.8.74.227 -> xxx.xxx.xxx.xxx DNS Standard query ANY isc.org
11.695449 xxx.xxx.xxx.xxx -> 194.8.74.227 DNS Standard query response RRSIG RRSIG DS DS NS ams.sns-pb.isc.org NS ns.isc.afilias-nst.info NS ord.sns-pb.isc.org NS sfba.sns-pb.isc.org
11.705516 194.8.74.227 -> xxx.xxx.xxx.xxx DNS Standard query ANY isc.org
11.705891 xxx.xxx.xxx.xxx -> 194.8.74.227 DNS Standard query response RRSIG RRSIG DS DS NS ns.isc.afilias-nst.info NS ams.sns-pb.isc.org NS sfba.sns-pb.isc.org NS ord.sns-pb.isc.org
11.723779 194.8.74.227 -> xxx.xxx.xxx.xxx DNS Standard query ANY isc.org
11.723787 194.8.74.227 -> xxx.xxx.xxx.xxx DNS Standard query ANY isc.org
11.723983 194.8.74.227 -> xxx.xxx.xxx.xxx DNS Standard query ANY isc.org
11.723989 194.8.74.227 -> xxx.xxx.xxx.xxx DNS Standard query ANY isc.org
11.724154 xxx.xxx.xxx.xxx -> 194.8.74.227 DNS Standard query response RRSIG RRSIG DS DS NS sfba.sns-pb.isc.org NS ams.sns-pb.isc.org NS ns.isc.afilias-nst.info NS ord.sns-pb.isc.org
11.724333 xxx.xxx.xxx.xxx -> 194.8.74.227 DNS Standard query response RRSIG RRSIG DS DS NS ord.sns-pb.isc.org NS sfba.sns-pb.isc.org NS ns.isc.afilias-nst.info NS ams.sns-pb.isc.org
11.724495 xxx.xxx.xxx.xxx -> 194.8.74.227 DNS Standard query response RRSIG RRSIG DS DS NS ams.sns-pb.isc.org NS ns.isc.afilias-nst.info NS sfba.sns-pb.isc.org NS ord.sns-pb.isc.org
11.724648 xxx.xxx.xxx.xxx -> 194.8.74.227 DNS Standard query response RRSIG RRSIG DS DS NS ams.sns-pb.isc.org NS ord.sns-pb.isc.org NS sfba.sns-pb.isc.org NS ns.isc.afilias-nst.info
11.725244 194.8.74.227 -> xxx.xxx.xxx.xxx DNS Standard query ANY isc.org
11.725256 194.8.74.227 -> xxx.xxx.xxx.xxx DNS Standard query ANY isc.org
11.725488 xxx.xxx.xxx.xxx -> 194.8.74.227 DNS Standard query response RRSIG RRSIG DS DS NS sfba.sns-pb.isc.org NS ord.sns-pb.isc.org NS ns.isc.afilias-nst.info NS ams.sns-pb.isc.org
11.725645 xxx.xxx.xxx.xxx -> 194.8.74.227 DNS Standard query response RRSIG RRSIG DS DS NS ns.isc.afilias-nst.info NS ord.sns-pb.isc.org NS ams.sns-pb.isc.org NS sfba.sns-pb.isc.org
See how this story progressed:
http://foxpa.ws/2010/07/21/thwarting-the-isc-org-dns-ddos/T
