blog / Jan 04, 2018

Mirai is Attacking Again, So We’re Outing its Hilarious, Explicit C&C Hostnames

by David Holmes

Warning: Explicit and potentially offensive content ahead.

The Mirai botnet is kind of like Madonna. They both were huge once, and then the adoring public shifted their attention to younger, newer acts but they keep on performing anyway. We wrote about Mirai extensively after we predicted its construction in our first IoT report, DDoS’s Newest Minions: IoT Devices in 2016.

Mirai has been in the news again recently. In December, Brian Krebs reported1 that two men had pleaded guilty as the co-authors of the IoT botnet. A new botnet, Satori (Japanese for “the awakening”) is a possible successor to Mirai. The source code for Satori was recently posted to Pastebin2 as a Christmas gift to the IoT hacker community. Like Reaper, Satori weaponizes exploits beyond simple brute-force default password guessing.3

F5 Labs and our data partner, Loryka, still monitor Mirai (but not Madonna, ha ha). Because even though Satori and Reaper might be the interesting new acts, Mirai and its children are still actively attacking from the Internet of Things. Our honeypots grab configurations from each botnet and we compile the list of command and control (C&C, a.k.a. C2 or CNC) hostnames that are used to control each bot. Attacks from the C&C host themselves are rare, but they make good indicators of compromise (IOC) because any requests for those hosts from inside a protected network can be traced back to the infected devices themselves.

So, we were looking through last quarter’s list of Mirai spinoff bots and all of their command and control (C&C) hostnames and had a bit of a laugh. Of course, we take this botnet stuff seriously, but we couldn’t help snickering a little at some of the domain names.

Of the 203 C&C hostnames we sampled in the last quarter of 2017, about 70 are still active in DNS. And of that original 203, 71% were registered (and almost certainly hosted) by Freenom, Namecheap (an Enom reseller), or Cloudflare. If you were a cybercriminal, why not use “free” domain registration services like Freenom for your C&C hosts? A simple Google search will tell you they care little about what you do with the domain as long as you use it (or they will eagerly park your domain and start collecting ad revenue). When it comes to domain registrars like Enom that offer reseller services to companies like Namecheap, the layers of domain management and orchestration from the registrant to the controller can make it harder to track down and process abuse complaints. Because cyber criminals know this, they often favor resellers instead of direct registrars. A simple Google search for Namecheap will turn up a history of complaints alleging they do little about abuse complaints, so it’s not surprising cyber criminals would chose to use them. Cloudflare, on the other hand, has drawn fire from Brian Krebs4 for their continued hosting of obvious DDoS-for-hire services.

Sure, the C&C list is a small sample size, and C&C hosts come and go quickly. This list is in no way exhaustive—it’s just a snapshot in time from last quarter. But for a breakdown of the domain hosting services, see the end of this article.

“Yes, I really am a C&C server.”

A disturbing number of the C&C servers brazenly scream out that they are, indeed, nefarious “cnc” servers. Check out this subset:

There’s a whole other category of hosts that identify not just as C&C servers, but as Mirai C&C servers. Thanks for the specificity, dudes! How much more obvious do you need to be?

For those of you security engineers out there, it’s probably not a terrible idea to flag any computer in your network that is looking up hosts that begin with “cnc” or “mirai.”

And somebody really likes boats. We like boats, too.

We’ve been saying that the Internet of Things is the attacker platform of the future. The world of IoT botnets is highly automated. And, of course, our defenses are getting more automated as well. It’s computers attacking and computers defending.

But every now and then you get a glimpse of the humanity buried in the morass of digital data. Take these cnc hostnames for example:

Sure, they’re completely juvenile, but that’s how you know they’re human. And humans make mistakes. Sometimes those mistakes are other humans, and those humans end up building IoT botnets controlled by C&C hosts whose names offend the senses or offer dubious advice.

What’s Up With All the .tk Domains?

In theory, the .tk top level domain (TLD) represents the Tokelau island chain of New Zealand, a place so small it doesn’t even have a regional airport. In reality, .tk domains are free and are used by the poor as well as a huge number of spammers, phishers, and stressors.5 The .tk TLD is now, incredibly, the third most popular after .com and .net. That’s right, more popular than .uk, .org, and .sex.

The massive popularity of .tk domains has increased the GDP of Tokelau by 10% and some of the increased revenue goes to provide the local poor their own Internet access. 6 Such a strange, circular world we live in.


Credit goes to the infosec community as 70% of the C&C hosts (including all of them with “cnc” in the hostname) are already offline. Cloudflare is still hosting about 7 of these hosts, down from the original 14.

Below is the list of hosts in table form. The second column denotes whether or not the host appears to still be active, at least from a network perspective.

Feel free to add these hosts to threat Intelligence IP reputation lists.

Mirai C&C Host Active 0 0 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 1 1 0 1 1 1 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 1 1 1 0 1 1 0 0
dns 0 0 1 0 0 0 0 0 0 0 0
f* 0 1 1 1 1 0 1 0 1 1 0 0
horsec* 0 1 0 1 1 1 0 1 1 0 1 1 0 1 1 0 1 1 1 0 1 0 0
lolzsecssh* 0 0 1 0 1 0 1 1 0 1 1 1 0 0 1 1 0 0 1 0 0 1 0 0 1 0 0 0 0 0 0 0
puti.csgo 0 0 1 1 1 0 0 0 1 0 0 0 1 1 0 0 0 1 0 0 0 0 0 0 0 1
test.cnc 0 1 0 1 1 1 0 0 0 0 0 0 0 1 0 0 1 0

MODIFIED: Feb 21, 2018

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