The slow brute zombies are back

Real-life zombies feed off weak passwords.

Regular readers will remember that late last year we saw a peculiar form of distributed bruteforce attack on certain ssh servers. What made this particular batch of failed login attempts stand out was that unlike the traditional rapid-fire bruteforce attempts we were quite adept at heading off with state tracking tricks (such as the OpenBSD PF method described here or a slightly different Linux-specific method), the technique seemed to be specifically designed to slip past such defenses.

I described the method and the evidence at some length in a series of colums, A low intensity, distributed bruteforce attempt (December 2, 2008), A Small Update About The Slow Brutes (December 6, 2008), Into a new year, slowly pounding the gates (December 21, 2008) and finally The slow brutes, a final roundup (January 22, 2009).

If you do not want to read through all of that, I'll recap: The traditional bruteforce attack is characterized by somebody trying again and again to find a combination of logon credentials (typically sets of user names and passwords) that will let them gain access to the system. The basic idea is that given enough tries, you will sooner or later find a user who has set a guessable password, and you have access.

One of the important weaknesses of the method is that the typical attacker would have gained access to only one or a few systems, and the attacker would then typically try to connect a lot more often than a typical user, and sysadmins learned to adapt their firewalls and other systems to lock out activity that fit the bruteforcer profile.

If you run a ssh service anywhere Internet-facing, you will be used to seeing a steady stream of failed logons for both existing and non-existing users. There's nothing new in seeing failed logons in your log files. However, what happened late last year was that we started seeing large numbers of failed ssh logon attempts, with the new twist that the same user would be trying to log on a large number of times, but never from the same place twice in rapid succession. This log data sample will give you an idea. The data will show you the pattern, as will the summary article.

Back then in January, my conclusion was that we had seen the conclusion of a largely failed experiment. After all, proceeding at a truly glacial pace and decreasing the number of attempts per user name as they went along hardly seemed like a recipe for success even if they could sneak past packet filtering based defenses.

It turns out I was wrong. Returning to my log summaries after taking a few days off from log data (yes, easter is big here, even moves geeks sometimes to take time off) I find data with almost exactly the same profile as last December's series.

This can only mean that there were enough successful attempts at guessing people's weak passwords in the last round that our unknown perpetrators found it worthwhile to start another round. For all I know they may have been at it all along, probing other parts of the Internet far from my unfashionable backwaters.

Anyway, they are most certainly back. A summary of the data so far follows in the concluding section. Please note that I would be very interested in communicating with other parties who see similar activity in their logs, and if you are responsible for one or more of the systems identified or you know who is, I urge you to take appropriate action.

The Data So Far

First, We Take root
The full log data reveal that they started rubbing up against my listening posts during the early hours of April 7th 2009 (as measured in CEST), concentrating first on the user root (attempts sorted by hostname here, hostnames here. Not terribly surprising that they tried to take on this one, as most Unix(ish) systems tend to at least have a root account.

Then We Take admin
After about twenty-four hours, the zombies in the cloud tired of root and turned their collective attention to admin (attempts sorted by hostname here, hostnames here. This is a user name I would not expect to be on a Unix syste by default. In my limited experience Microsoft systems tend to use this one more often, but then there may be enough of those systems out there with a SSH service and weak passwords out there to try.

And james Will Make Us Famous
Well into civilized lunchtime (CEST) on April 9th, our would-be guests turned their attention to james (attempts sorted by hostname here, hostnames here. Why this user name received so much attention is a complete mystery to me. They did tire in the end, though.

Before We Turn To 123456, aadi And The Rest Of The Rabble
As if to confirm that we are indeed seeing a rerun of last November and December's sequence of events, the robots started on their regular alphabetic attempts on April 11th:

Apr 11 17:44:15 rosalita sshd[51241]: error: PAM: authentication error for illegal user james from 221.130.177.154
Apr 11 17:50:47 rosalita sshd[51258]: error: PAM: authentication error for illegal user 123456 from 220.194.54.41
Apr 11 17:53:24 rosalita sshd[51262]: error: PAM: authentication error for illegal user 123456 from webmail.sistemafieg.org.br
Apr 11 17:58:25 rosalita sshd[51285]: error: PAM: authentication error for illegal user 123456 from 202.82.25.161
Apr 11 18:00:59 rosalita sshd[51307]: error: PAM: authentication error for illegal user aadi from mail.cgconsultoriacontabil.com.br
The various comments to my earlier columns tended to point out the near-futility of low-intensity bruteforcing, and I took the fact that the last series of attempts did not run to the end of the alphabet as an indication that the perpetrators themselves had reached the same conclusion.

Now we know that they just moved on, went elsewhere for a while and now they're back. In the meantime, they must have hit on enough weak minds and associated weak passwords that they were able to take over and zombiefy enough systems to be worth their while.

The data so far (collected up to April 12, 2009, roughly 21:00 CEST) indicates that the total number of hosts involved in the attempts at my listening posts is just over a thousand (a list of hosts available here).

It is probably worth repeating that in real life, zombies feed on both weak minds and weak passwords.

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If you found this article useful, enjoyable or irritating, please drop me a line. Material related to this article is available for free via links from my web space. Some additional material will be made available for reasonable research purposes. If you want more extensive assistance, please contact me (via email or other means) to make arrangements.

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Also worth noting, I will be doing a PF tutorial at BSDCan 2009 in May, and I will be staying around for the rest of the conference. I look forward to seeing you there.


Note: A Better Data Source Is Available
Update 2015-04-02: For a faster and more convenient way to download the data referenced here, please see my BSDCan 2013 presentation The Hail Mary Cloud And The Lessons Learned which summarizes this series of articles and provides links to all the data. The links in the presentation point to a copy stored at NUUG's server, which connects to the world through a significantly fatter pipe than BSDly.net has.

Oh yes, you signed up for this. You did. Honest.

Honesty in marketing. You may have heard of it.

It may come as a surprise to some, but I generally do not spend much time on spam related matters. Occasionally I need to do some manual labor to keep spamd and spamassasin in trim, but at most times my little robot helpers just keep running, leaving my desktop essentially spam free.

That changed slightly late last month. Messages hawking the oddest wares started arriving, with a largish number of messages claiming that I had actually signed up to receive them:

You are receiving this message because on 2/26/2009 at 3:57 PM peter@bsdly.net 64.12.116.10 registered to receive messages from e-researchcouncil.com and its partners. To change your preferences with e-researchcouncil.com, go to the website and select "Contact Us" to review your options.

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Note: This piece is also available without trackers but classic formatting only here because a linkedin post by Paul Vixie in July 2025 reminded me I had written this way back when.

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To give you an idea how likely that statement is to be true, consider this: The 64.12.116.10 address resolves back to somewhere in America Online's network, pretty much an ocean and then some away from where I'm usually located.

I assume entering my address into a few web forms is somebody's idea of a joke, and the net effect was that a number of spammy messages started appearing in my mailbox, starting on February 27th. Only about third of the messages contained that particular claim, and a typical message would contain headers like these:

X-From-Line: eHarmonyDating@BranchSprint.com Fri Feb 27 16:30:36 2009
Return-path: <3f5.4.73479158-21937306@BranchSprint.com>
Envelope-to: peter@bsdly.net
Delivery-date: Fri, 27 Feb 2009 19:15:13 +0100
Received: from [99.198.152.161] (helo=dns7-cronomagic-biz.BranchSprint.com)
by skapet.bsdly.net with esmtp (Exim 4.69)
(envelope-from <3f5.4.73479158-21937306@BranchSprint.com>)
id 1Ld7Eu-00074N-NF
for peter@bsdly.net; Fri, 27 Feb 2009 19:15:13 +0100
X-Gnus-Mail-Source: pop:peter@bsdly.net
Message-Id: <KKcbjdhdagmcfbVN@BranchSprint.com>
Reply-To: <eHarmonyDating@BranchSprint.com<
From: eHarmonyDating <eHarmonyDating@BranchSprint.com>
Subject: eHarmony could match you with the right singles
Date: Fri, 27 Feb 2009 16:30:36 GMT
X-Information: 73479158_21937306 ListZA251
X-Complaints-To: <complaints@BranchSprint.com>
To: <peter@bsdly.net>
My first impulse was, in case this is an honest mistake somewhere, let's try and play nice at first. That meant sending messages to the X-Complaints-To: addresses and waiting to see what would happen.

You should not be terribly surprised to hear that those addresses all turned out to be invalid, the messages undeliverable.

In the meantime, I went on collecting messages, and the amount of data I had accumulated was large enough that I could reach some preliminary conclusions.

It's obvious that in order to reach me, the messages would need to clear greylisting and avoid triggering too many of my spamassassin rules. That meant in turn that the messages were sent using real mail servers. So I started collecting the messages with that claim for further study. The messages were almost all sent from a few distinct subnets, all of them apparently fairly well stocked with real mailservers.

Based on data from the spam messages and whois lookups and the larger groupings of messages, the professional spammers are, for your convenience in case you want to visit them:

NN, LLC
4001 Kennett Pike
Suite 134-910
Greenville, DE 19807
US

Spiesigma PLC
P.O. BOX 243, 2221 S Webster Ave
Green Bay, WI 54301
US

GreenButtonMedia.com
5580 La Jolla Blvd # 73
La Jolla, CA 92037
US

AdSelectMedia.com
5482 Wilshire Blvd. #302
Los Angeles, CA 90036
US

BestOnlineGreetings.com
5482 Wilshire Blvd. #302
Los Angeles, CA 90036
US

MyPromotionNetwork.com
970 West Valley Parkway
Suite 604
Escondido, CA 92025

GreatTechsOnline.com
5580 La Jolla Blvd # 73
La Jolla, CA 92037
US

CrownVenturesMedia.com
7127 Hollister Ave., Suite 25A, #145
Goleta, CA 93117

Top Notch Media, Inc.
1735 Market Street · Suite A · PMB 429
Philadelphia, PA 19103-7588

In addition, some of the domain names used in the spam messages were registered via an anonymizing service whose whois data comes out as:

Dynamic Dolphin Privacy Protect
5023 W 120th Ave #233
Broomfield
null,80020

The spam volume from all of them swelled at roughly the same time, so it is likely that they cooperate on keeping their lists up to date.

So we see spammers evolving: They buy or rent real mail servers now and they have even started coordinating. Using greylisting has actually increased the cost of becoming a successful spammer.

At our end of the game, we stay ahead of their game thanks to tools like spamd, and several of us dump and share our greytrap lists. It is even possible to collect IP addresses and feed a large number at the time to spamdb, but after a little while I grew tired of the increased manual work decided it was time for a counterprank. Cleaning up after spammers is no fun, unless you can have little robot helpers do the heavy lifting.


The Counterprank: A Feedback Loop
Regular readers will remember that I have a collection of known bad addresses in my domains that I use for my greytrapping, all generated elsewhere, that has come in handy at times. Run of the mill spam operators tend to just suck in anything that looks like email addresses, and keeping the list available on the web has served us extremely well here.

The professional spammers are apparently not quite that stupid, so the problem became a little different. They were able to sneak past greylisting and conventional content filtering. Also, they were apparently oblivious to email communication and as far as I can tell their Unsubscribe pages are not entirely believeable.

So it was a relief to find that places such as http://e-researchcouncil.com/ are very happy to accept any email address you can come up with. Time to enlist a few of our imaginary friends, drawn from the obvious source.

I did ponder the ethics for a few moments. After all, the forms included sentences such as "I certify that I am a US citizen", which was about as true as the assertion that I had signed up via an AOL proxy. But I did not ponder that matter for long. Moments later, most of the spam operators found themselves with new neighbors with odd names and foreign email addresses.

The net result is that the hosts start appearing automagically in the hourly dump of my list of greytrapped addresses and in the daily spamd activity report. With a little luck, we have succeeded in increasing the cost of spamming one tiny increment.

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If you found this article useful, enjoyable or irritating, please drop me a line. Material related to this article is available via links from my web space. Some additional material will be made available for reasonable research purposes. If you want more extensive or non-trivial assistance, please contact me (via email or other means) to make arrangements.

Note that the list of greytrapped addresses is updated ten past every full hour, fetching it every minute like some Americans have started doing is not a good use of your resources.

What have the black boxes wrought

How compartmentalization turned into a security disaster. Greed, incompetence and dishonesty was involved. 

IT security or the lack of any such thing has grabbed headlines lately here in Norway. A series of high profile public institutions have seen large scale worm infections on their Microsoft based networks. 

Late last year the regional government agency responsible for essentially all health care in the western part of the country had a worm infection so bad they essentially shut down their network as a preventive measure. 

During the last few weeks, the national police force, of all thinkable organizations, has seen not one, but two large-scale incidents. Use of Microsoft products and sloppy system maintenance are both pervasive enough that similar incidents are likely happening right now elsewhere, somewhere near you too. 

The news reports about the Norwegian police force's IT problems contained one item that was particularly shocking to IT types like me: 

Apparently large parts of the bureaucracy that is responsible for the confidential and correct processing of criminal matters and all sorts of sensitive personal information associated with the crimes runs essential services on Microsoft Windows NT 4.0. 

That version of the Microsoft product is so old it is officially abandonware, and early reports of the police network problems included the oldish news that even the antiware vendors have stopped supporting the system. 

Later reports had police IT department officials claim that the worm infections were not that much of a security problem, since at this point all the worm actually did was spread. Break out the popcorn, boys and girls: In an upcoming episode, we will see how the worm infected Windows machines the Royal Norwegian Police did not find or couldn't clean well enough are used in the perpetration of some cybercrime or other. 

 It's all pretty sickening, and at this point it would be rather tempting to spend the rest of the column ranting about the general stupidity of Windows users. But a smarter approach is to see if there is a lesson to be learned. 

To do that, we need to backtrack quite a bit and look at the cult of the little black boxes. 

The cult of the little black boxes, and Microsoft the 1980s corporation 

We need to go back and take in what the world was like in the nineteen-eighties. This was back when the world was divided into real computers (from the likes of IBM, Digital, and regional quasi-monopolies like our own Norsk Data) and those annoying toys called 'personal' microcomputers, where the 'IBM PC compatibles' had emerged as the surprise leader of the pack. 

Computer networks were usually private, corporate things and rarely interconnected much, with the rare exception of those institutions that were part of the US Department of Defense science experiment that was becoming known variously as ARPANET or 'the Internet'. 

If you took your programming classes back in the nineteen-eighties, you likely know that we were taught that black boxes were good. 

Compartmentalization was the order of the day, meaning that as a developer you were supposed to create code with a well defined inteface, so anybody interacting with your code would be presented with a cleanly predictable result to any given input. 

Your code should be a black box and for any particular specificiation there could be written several interchangeable modules to fit the bill. 

So far so good, predictability is nice and with compartmentalization comes, we hope at least, clear chains of responsibility. 

But several factors combined to take the cult of the black boxes and turn it into a corporate culture at a corporation that was growing from a handful of furry hackers into a corporation at the time, namely Microsoft. 

Microsoft' early successes all came from writing software for single-user systems that were so limited that working around the limitations of the hardware became much of a lifestyle. 

At the start of the decade, networking on microcomputers in Microsoft's range was pretty much out of the question, and by the end of the eighties any sort of connectivity (even dial-up) was still an expensive optional extra that was still too hard to configure for most people. 

On the storage side, we progressed from 128 kilobyte floppies to hard drives of just over a hundred megabytes for personal systems, with the 32 megabyte partition size still a very present limiting factor.

Amazing developments all, but both the applications and the organization grew faster than the hardware could keep up with. 

The organization now had several levels of management, and each one demanded maximum productivity from their underlings. 

Keeping in mind that each programmer or team would be writing little black boxes anyway, it made perfect sense to set up the software production line so each developer only had access to those parts of the system he or she was supposed to be working on. 

That way developers would be concentrating on their main task and minimize time spent waiting for compiles to finish. At predetermined times the developers would then upload the source code for their little black boxes to a central build system. 

The only people who had all the parts of the projects were in fact the custodians of the build system. 

Source code version control systems were made part of the process, but there is anecdotal evidence that the transition from standalone hacking to a version control regime was a rough one for many early Microsoft developers. 

Only a few days ago I offered pretty much the content of the last few paragraphs to a table of youngish free software developers over beer. 

The reaction was quick an unanimous: 

"That way, nobody really knows what's going on in the software". 

That is a very valid point, and it proves how far we've come with free software. 

At the same time there is every reason to believe that the extreme compartmentalization that Microsoft established for its product development in the 1980s was the way things were done there until very recently, if indeed it has changed at all. 

By the mid-1990s when Microsoft had been dragged kicking and screaming into modern-day network environments, and the ongoing saga of internet-enabled malware started in earnest (I've written a summary in a malware paper -- an updated version is available here), with the company moving from early denial of any bugs whatsoever through a near-constant barrage of emergency hotfixes to today's monthly megapatch regime. 

With the source code still a closely guarded (if occasionally leaked) secret, there is really no way for us to know if they've learned any lessons at all. 

One indication that they still have some way to go is this Infoworld article about the state of their protocol documentation (summary: it's not to be trusted at all). As for the state of the source code, all we can do is to study the flow of urgent patches. 

Much better then to learn how it should be done - Say from Theo de Raadt's AsiaBSDCon 2009 presentation about how OpenBSD's release process works, and if you want more of the gory details, do check his classic exploit mitigation presentation. Also, most likely you could do worse than read Damien Miller's OpenSSH security presentation (full text here). 

It's all those little things we do, at FreeCode and in free software in general. If you found this column useful, entertaining or irritating, please drop me a line.

The slow brutes, a final roundup

The slow brutes stopped their churning. Their last call was for sophia.

Over the last few columns, we have followed the progress of what appears to be a botnet cloud's attempt at gaining access to a couple of FreeBSD machines I have in my care. One of my predictions about the distributed, slow ssh bruteforce attempts we started seeing in November of 2008 was that at the rate they were going at the time, it would be well into the new year before we would see the end of their alphabetic progression. As it turns out, they stopped just before year end, before even reaching the 'T's. The last attempt recorded was this:

Dec 30 11:09:03 filehut sshd[54981]: error: PAM: authentication error for illegal user sophia from static-98-119-110-139.lsanca.dsl-w.verizon.net

The full collection of raw data is available here, with a .csv summarising number of attempts, user names and hosts per day here.

With the incident apparently over, we can sit back and study the data and see what patterns emerge.

The anatomy of the attack
There are a number of ways to slice and dice the data. One useful way to view the collection is to do day to day statistics, such as the ones in this .csv file, numbers extracted by some simple greping and awkery. Based on the day to day data, I made this graph to illustrate the progression.



Then for your data overload cravings, I turned the same data to a log scale for enhancement and added number of attempts -



hopefully adding some insight into just what happened when and maybe supporting some guessing about what they were indeed trying to achieve.

It is possible that we missed the actual start of those coordinated attempts, but the data we do have show a few interesting points.

The earliest preserved data from November 19th shows the most attempts per user name (average 13.29), with 7 unique user names tried and a relatively low number of hosts (76).

On November 20th, the cloud turned its attention to one user, root, trying only that user name a total of 1697 times from 566 different hosts. It would be well into November 21st before the cloud moved on to admin (128 attempts, 107 different hosts) and an apparently coordinated alphabetic progression.

The absolute number of attempts and hosts involved per day fell quickly, with average number of attempts per user name stabilizing at a fairly low number after a few days. The exception is the peak on December 27th, which could perhaps be explained by owners of compromised computers returning from holiday celebrations and turning their computers back on. The sharp decline in all numbers over the next few days before the attempts stop seems consistent with what we assumed: That the botnet masters were allocating resources according to likelihood of success.

So why is this incident important, or even interesting? After all, attempts to gain access to services by brute force or dictionary based attacks are nothing new. I was rather intrigued to see clear evidence that miscreants were trying to find the way under the radar of intrusion detectors by distributing the intrusion task over a large number of hosts. If their success rate at my sites is anything to go by, this may be just a weird anomaly and an idea that did not lead anywhere. I haven't heard from anybody who was actually compromised by this particular set of clouds, but then again anybody who got bitten would likely be rather shy about telling the world at large or even fairly obscure researchers about the fact.

Always looking for patterns I even went to the trouble of extracting some data from the logs about the individual hosts that participated in the attack. After some basic shell gymnastics I ended up with a .csv of hostnames, number of attempts from the host as well as the date of first and last contact (available here). Next I tried (and failed - gnuplot gurus, here's your chance) to graph the data usefully in OpenOffice, but ended up with a sorted version (sorted by attempts, start and end date) that at least shows us that a surprising number of hosts actually hung on for most of the time the coordinated attepts went on.

The lessons learned: security the old-fashioned way

The general lesson of this incident is rather predictably that miscreants will occasionally try new and original ways to try to crack their way into your system. The slow method was a refreshing variation, and for all we know they may have succeeded in places where the people in charge remain blissfully unaware. Trying to catalogue and detect all kinds of variations on the theme of "attempts at unauthorized access" is the kind of activity that has kept "antivirus" people in beer money for quite a while, and if there is a lesson to be learned here, it is that trying to enumerate badness (Yes, do look it up using your favorite search) is a losing game. Make sure whatever system you run is sanely constructed, any bugs that do turn up are fixable within a reasonable time frame, and so on. I suppose I will come back later with a rant about how much damage the "black boxes" school of thinking about software has done, especially after it got elevated to practically religious dogma by certain major players. And yes, you can usefully look that up as well.

For those of you who are interested in the data, here are the now complete extracts for your perusal:

The full set of log data
The per day .csv file - and the same in an .ods sheet with some graphing attempts
Per host data in the "Host,Attempts,StartDate,EndDate" format and sorted by attempts, start and end

For those of you interested in learning about OpenBSD and related delights like PF, FreeCode is set to start offering courses featuring among others yours truly as well as the usual support and consulting offerings. Contact the good front end people at FreeCode for further details.

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International readers are at liberty to ignore the following, but Norwegian online IT magazine digi.no are apparently in the process of setting up a sort of census of Norwegian bloggers. The following is there to make this blog show up in their listing. You can read their article about the initiative (Norwegian only, unfortunately).

Note: A Better Data Source Is Available
Update 2013-06-09: For a faster and more convenient way to download the data referenced here, please see my BSDCan 2013 presentation The Hail Mary Cloud And The Lessons Learned which summarizes this series of articles and provides links to all the data. The links in the presentation point to a copy stored at NUUG's server, which connects to the world through a significantly fatter pipe than BSDly.net has.

Into a new year, slowly pounding the gates

The distributed but clearly coordinated bruteforcers are still at it. How long until they reach the end of the alphabet? And why are they staying away from my OpenBSD machines? Are we seeing the contours of a controlling intelligence?

As large parts of the Western world prepares for the holidays, the swarm of little robots that started trying to pry open the doors to my machines some weeks back are still at it. As far as we can tell, the coordinated attempts started some time in early November or perhaps late October (we don't keep logs around for long enough to be sure), with an alphabetic progression that has now progressed to somewere into the os. The complete listing from the time I started noticing up to the time I started writing this column can be found here.

I've written about this before, and in fact one of those columns was slashdotted, a pleasant surprise to me and a cause of some excitement among my colleagues at FreeCode.

After writing that article, I did some further research and found out that a precursor to what we are seeing now was observed as early as May 2008, as described in an Ars Technica article published at the time. That article also reveals, via Linuxtoday, that yours truly was among the many who failed to understand the problem, at least for a while. Then again, maybe actual log excerpts would have helped.

The problem, such as it is, seems to be that a somebody who herds a botnet has decided that the laws of big numbers favors those who keep trying for long enough. User names and passwords are generally far enough from random that if you are allowed to go on for long enough, you will sooner or later manage to guess a correct combination of username and password and get access to a machine somewhere.

Sysadmins have been seeing bruteforce attacks for years. The traditional brute force attack would be a rapid succession of login attempts from one host, and usable countermeasures were devised in short order. My favorite of course involves PF, and the description of how to thwart traditional bruteforcers is one of the more popular pages in my PF tutorial.

The distributed, slow bruteforcers are different. For one, the login attempts from each host out in the cloud are spaced far enough apart in time that intrusion attmpt detectors will not trigger. Next, it takes a keen eye to spot the common thread in the attempts spaced up to a number of minutes apart: a monotonously alphabetic progression of user names, with attempts coming in from different hosts. Some number of attemtps at a specific user name, before the cloud moves on the next one, in alphabetic order.

During the period we have been observing the slow brute activity, a total of 695 hosts have been involved. A total of 665 hosts made unsuccessful attempts at authenticating at the hosts we are observing during November, while the number for December so far is 346. The typical number of attempts per user name has decreased, too, from a typical ten do fifteen during the early days down to between one and four during the last couple of weeks.

I thought at first that the decrease in activity was just an indicator that compromised hosts were getting cleaned up, but my colleague Egil Möller was the first to suggest that since we know the attempts are coordinated, it is not too far fetched to assume that the controlling system measures the rates of success for each of the chosen targets and allocates resources accordingly.

If Egil's assumption is right, we are seeing the bad guys adapting. My systems do not run any services they do not need to, and apparently all attempts at gaining access have been futile so far. So, the controlling system shifts resources to elsewhere, even if the access attempts do not stop entirely. Come to think of it, I'm not seeing any attempts at all on my OpenBSD systems, so it is possible to speculate that whoever is behind this phenomenon has decided that OpenBSD systems are hardened enough to begin with and usually run by compentent paranoids as to be useless as targets. That would be a comforting thought at the end of a long and sometimes trying year.

Speaking of the new year, look for exciting announcements coming from FreeCode. We're working on some cool things. And with a bit of luck, I might run into you at one conference or the other during the coming year.

Happy holidays to everyone.


Note: A Better Data Source Is Available
Update 2013-06-09: For a faster and more convenient way to download the data referenced here, please see my BSDCan 2013 presentation The Hail Mary Cloud And The Lessons Learned which summarizes this series of articles and provides links to all the data. The links in the presentation point to a copy stored at NUUG's server, which connects to the world through a significantly fatter pipe than BSDly.net has.

A Small Update About The Slow Brutes

Slow and steady might actually do it, eventually.

The reactions to my December 2nd column hit me with a bit of surprise. The column was taken on by slashdot and Linux Today both, producing a largish number of page views, but only two clicks on my featured ads. But while my clickthrough rate is not particularly interesting to others, the comments to the columns sometimes are.

If you look at the comments at slashdot and elsewhere, most of the commenters most likely did not actually read the column in full or did not take the time to digest what it actually said, with some notable exceptions. And yes, there were others, some also wrote in via email with informed comment - thanks!

For the benefit of those who did not get the point the first time around, I'll try once more to explain what the observations are and what they may in fact mean.

A number of commenters offered well meant advice to use packages like fail2ban, denyhosts or a few others.

The common denominator for all of them is that they track single hosts that make a larger than usual number of connections or are the source of a number of failed logins higher than a certain threshold value over a set time period. I appreciate your concerns, but the subject of the column did not fit well with the way those the packages work.

In fact, a similar scheme was already in place at the site that provided the data. The machines that provided the ssh logs are FreeBSD ones (as the sharper ones have observed already, and the reasons may possibly be revealed over beer sometime), but any gateway under my control will run OpenBSD, and by extension, PF (and yes, there is a book you might want to order from one (North America) or the other (Europe and elsewhere) of the OpenBSD project's sites). For a quick fix of background, the online PF tutorial may be worth a look.

Anyway, the /etc/pf.conf at that site's gateway contains the lines

table <abusive_hosts> persist
block log quick from <abusive_hosts>
and

pass log (all) quick proto { tcp, udp } from any to any port ssh flags S/SA keep state \
(max-src-conn 15, max-src-conn-rate 7/3, overload <abusive_hosts> flush global)

Those lines provide a variation on the logic that those posters recommended. Essentially, any host that tries 15 or more simultaneous ssh connections, or come in at a rate of more than seven over the span of three seconds, will be added to the table <abusive_hosts>, and the block quick rule blocks any further access from those hosts. Yes, flush global means what you think it does.

This works at the network level. For a gateway with a potentially large number of hosts on either side, the success or otherwise of eventual authentication may not be relevant and may be better dealt with elsewhere. Anyway, at the time I started working on this column, the table <abusive_hosts> on the gateway contained only two hosts:

:~$ sudo pfctl -t abusive_hosts -v show
194.204.37.93
201.57.187.114
I keep offenders in that table for 24 hours only, I do not believe in the permanent bans that some commenters advocate. After all, there is such a thing as DHCP, and entire netblocks are reallocated with amazingly short intervals.

Anyway, looking at the authentication log on the gateway reveals how those hosts got added to the the table in the first place:

:~$ grep 194.204.37.93 /var/log/authlog
Dec 5 22:50:30 delilah sshd[15266]: Did not receive identification string from 194.204.37.93
Dec 5 22:50:37 delilah sshd[6106]: Did not receive identification string from 194.204.37.93
Dec 6 01:29:58 delilah sshd[30359]: Failed password for root from 194.204.37.93 port 47071 ssh2
Dec 6 01:29:58 delilah sshd[7293]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:29:59 delilah sshd[4395]: Failed password for root from 194.204.37.93 port 47296 ssh2
Dec 6 01:29:59 delilah sshd[27615]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:00 delilah sshd[12248]: Failed password for root from 194.204.37.93 port 47330 ssh2
Dec 6 01:30:00 delilah sshd[24579]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:01 delilah sshd[3434]: Failed password for root from 194.204.37.93 port 47380 ssh2
Dec 6 01:30:01 delilah sshd[32737]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:02 delilah sshd[11984]: Failed password for root from 194.204.37.93 port 47425 ssh2
Dec 6 01:30:02 delilah sshd[27059]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:03 delilah sshd[13345]: Failed password for root from 194.204.37.93 port 47459 ssh2
Dec 6 01:30:03 delilah sshd[1858]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:04 delilah sshd[12739]: Failed password for root from 194.204.37.93 port 47516 ssh2
Dec 6 01:30:04 delilah sshd[16843]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:05 delilah sshd[13796]: Failed password for root from 194.204.37.93 port 47564 ssh2
Dec 6 01:30:05 delilah sshd[16789]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:06 delilah sshd[628]: Failed password for root from 194.204.37.93 port 47602 ssh2
Dec 6 01:30:06 delilah sshd[6162]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:07 delilah sshd[2579]: Failed password for root from 194.204.37.93 port 47646 ssh2
Dec 6 01:30:07 delilah sshd[12461]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:08 delilah sshd[12725]: Failed password for root from 194.204.37.93 port 47685 ssh2
Dec 6 01:30:08 delilah sshd[29909]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:09 delilah sshd[16560]: Failed password for root from 194.204.37.93 port 47724 ssh2
Dec 6 01:30:09 delilah sshd[1690]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:09 delilah sshd[1600]: Failed password for root from 194.204.37.93 port 47771 ssh2
Dec 6 01:30:09 delilah sshd[28882]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:10 delilah sshd[29953]: Failed password for root from 194.204.37.93 port 47807 ssh2
Dec 6 01:30:10 delilah sshd[15349]: Received disconnect from 194.204.37.93: 11: Bye Bye
Dec 6 01:30:11 delilah sshd[2962]: Failed password for root from 194.204.37.93 port 47845 ssh2
Dec 6 01:30:11 delilah sshd[27557]: Received disconnect from 194.204.37.93: 11: Bye Bye
and

:~$ grep 201.57.187.114 /var/log/authlog
Dec 5 23:55:30 delilah sshd[24338]: Did not receive identification string from 201.57.187.114
Dec 5 23:55:35 delilah sshd[23570]: Did not receive identification string from 201.57.187.114
Dec 5 23:59:58 delilah sshd[10216]: Invalid user raimundo from 201.57.187.114
Dec 5 23:59:58 delilah sshd[10216]: Failed password for invalid user raimundo from 201.57.187.114 port 35776 ssh2
Dec 5 23:59:58 delilah sshd[18515]: Received disconnect from 201.57.187.114: 11: Bye Bye
Dec 6 00:00:01 delilah sshd[17353]: Invalid user joan from 201.57.187.114
Dec 6 00:00:01 delilah sshd[17353]: Failed password for invalid user joan from 201.57.187.114 port 37570 ssh2
Dec 6 00:00:02 delilah sshd[30314]: Received disconnect from 201.57.187.114: 11: Bye Bye

which again shows that these were the old-fashioned, rapid-fire kind of bots. Looking a bit closer even reveals that they kept trying after they were put in the doghouse:

:~$ sudo pfctl -t abusive_hosts -vT show
194.204.37.93
Cleared: Sat Dec 6 01:30:11 2008
In/Block: [ Packets: 18985 Bytes: 835336 ]
In/Pass: [ Packets: 0 Bytes: 0 ]
Out/Block: [ Packets: 0 Bytes: 0 ]
Out/Pass: [ Packets: 0 Bytes: 0 ]
201.57.187.114
Cleared: Sat Dec 6 00:00:02 2008
In/Block: [ Packets: 800 Bytes: 48268 ]
In/Pass: [ Packets: 0 Bytes: 0 ]
Out/Block: [ Packets: 0 Bytes: 0 ]
Out/Pass: [ Packets: 0 Bytes: 0 ]

And of course there were no traces of those IP addresses or corresponding host names in the authentication logs in the machines where I have collected the data about slow bots. My best guess at why is that the gateway's IP address is at the low end of the routable range for that site. Note to bruteforcers: try working the Internet in reverse next time. (Not that it would help much here, but that's another story.)

The reason why I don't see much activity for other services is simply that those machines do not run all that many services, and only the services they actually run for the world's benefit are in fact available to the outside.

My log data shows a definite pattern, and the alphabetic progression points to a degree of coordination. The slow bots are, I theorize, operated by a botnet herder who has a large pool of compromised hosts available and who also believes that given enough time, sooner or later you will find a correct combination of user names and passwords for a given host. Statisticians tell me that assumption is in fact valid, at least to some extent.

By setting up the necessarily large number of attempts to come from a sizable number of hosts in either round-robin or pseudo-random order and intervals for each individual host's attempts in the several minutes to hours range, there is a very real possibility that the slow but determined campaign for control of any single system will drown in the noise.

It is useful to keep in mind that malware moved out of the hands of pranksters and vandals years ago. Mass destruction of systems or data might still make the occasional headline, but staying out of the limelight is likely to be a lot more profitable. Modern malware masters want their creations and charges to stay undetected. What we may be seeing right at this moment is that they have realized the herd may only be sustainable if they grow it slowly.

---

If you are interested in researching the phenomena I've blogged about, you're welcome to contact me directly for more information or raw data.


Note: A Better Data Source Is Available
Update 2013-06-09: For a faster and more convenient way to download the data referenced here, please see my BSDCan 2013 presentation The Hail Mary Cloud And The Lessons Learned which summarizes this series of articles and provides links to all the data. The links in the presentation point to a copy stored at NUUG's server, which connects to the world through a significantly fatter pipe than BSDly.net has.

A low intensity, distributed bruteforce attempt

We have seen the future of botnets, and it is a distributed, low-key affair. Are sites running free software finally becoming malware targets?

Note: This piece describes illegal activity I detected in 2008, targeting SSH servers. Later pieces in this series would hint at the existence of a specific piece of Linux malware, which I had not identified at the time this piece was written.

NOTE: A version without trackers but “classical” formatting is available here.

Phase 1: “That's odd …”
During the last few weeks, I noticed an anomaly in the authentication logs on one of my listening posts. There were a larger than usual number of ssh login attempts overall, a higher than usual number of attempts for non-existent user names as well as some failures for a few that actually exist as well.

Looking at the log directly a typical progression would look like this:

Nov 19 15:04:22 rosalita sshd[40232]: error: PAM: authentication error for illegal user alias from s514.nxs.nl
Nov 19 15:07:32 rosalita sshd[40239]: error: PAM: authentication error for illegal user alias from c90678d3.static.spo.virtua.com.br
Nov 19 15:10:20 rosalita sshd[40247]: error: PAM: authentication error for illegal user alias from 207-47-162-126.prna.static.sasknet.sk.ca
Nov 19 15:13:46 rosalita sshd[40268]: error: PAM: authentication error for illegal user alias from 125-236-218-109.adsl.xtra.co.nz
Nov 19 15:16:29 rosalita sshd[40275]: error: PAM: authentication error for illegal user alias from 200.93.147.114
Nov 19 15:19:12 rosalita sshd[40279]: error: PAM: authentication error for illegal user alias from 62.225.15.82
Nov 19 15:22:29 rosalita sshd[40298]: error: PAM: authentication error for illegal user alias from 121.33.199.39
Nov 19 15:25:14 rosalita sshd[40305]: error: PAM: authentication error for illegal user alias from 130.red-80-37-213.staticip.rima-tde.net
Nov 19 15:28:23 rosalita sshd[40309]: error: PAM: authentication error for illegal user alias from 70-46-140-187.orl.fdn.com
Nov 19 15:31:17 rosalita sshd[40316]: error: PAM: authentication error for illegal user alias from gate-dialog-simet.jgora.dialog.net.pl
Nov 19 15:34:18 rosalita sshd[40334]: error: PAM: authentication error for illegal user alias from 80.51.31.84
Nov 19 15:37:23 rosalita sshd[40342]: error: PAM: authentication error for illegal user alias from 82.207.104.34
Nov 19 15:40:20 rosalita sshd[40350]: error: PAM: authentication error for illegal user alias from 70-46-140-187.orl.fdn.com
Nov 19 15:43:39 rosalita sshd[40354]: error: PAM: authentication error for illegal user alias from 200.20.187.222
Nov 19 15:46:41 rosalita sshd[40374]: error: PAM: authentication error for illegal user amanda from 58.196.4.2
Nov 19 15:49:31 rosalita sshd[40378]: error: PAM: authentication error for illegal user amanda from host116-164.dissent.birch.net
Nov 19 15:55:47 rosalita sshd[40408]: error: PAM: authentication error for illegal user amanda from robert71.lnk.telstra.net
Nov 19 15:59:08 rosalita sshd[40412]: error: PAM: authentication error for illegal user amanda from static-71-166-159-177.washdc.east.verizon.net
Nov 19 16:02:06 rosalita sshd[40455]: error: PAM: authentication error for illegal user amanda from host87-163-static.30-87-b.business.telecomitalia.it
Nov 19 16:05:08 rosalita sshd[40459]: error: PAM: authentication error for illegal user amanda from 213.150.184.70
Nov 19 16:08:16 rosalita sshd[40465]: error: PAM: authentication error for illegal user amanda from mail.pddsl.de
Nov 19 16:11:24 rosalita sshd[40486]: error: PAM: authentication error for illegal user amanda from abu66.internetdsl.tpnet.pl
Nov 19 16:15:00 rosalita sshd[40491]: error: PAM: authentication error for illegal user amanda from 125.77.106.246
Nov 19 16:17:43 rosalita sshd[40497]: error: PAM: authentication error for illegal user amanda from 217.76.34.230
Nov 19 16:20:54 rosalita sshd[40506]: error: PAM: authentication error for illegal user amanda from robert71.lnk.telstra.net
Nov 19 16:24:09 rosalita sshd[40529]: error: PAM: authentication error for illegal user amanda from p578b4f0b.dip0.t-ipconnect.de
Nov 19 16:28:11 rosalita sshd[40538]: error: PAM: authentication error for illegal user amanda from mail.carena-ci.com
Nov 19 16:30:15 rosalita sshd[40551]: error: PAM: authentication error for illegal user amavis from 87.229.3.89
Nov 19 16:34:31 rosalita sshd[40567]: error: PAM: authentication error for illegal user amavis from 218.248.79.251
Nov 19 16:36:40 rosalita sshd[40574]: error: PAM: authentication error for illegal user amavis from 83-103-70-170.ip.fastwebnet.it
Nov 19 16:40:05 rosalita sshd[40596]: error: PAM: authentication error for illegal user amavis from 75-49-251-71.lightspeed.snjsca.sbcglobal.net
- and so on, with a striking regularity. See for example the attempts to log on as the alias user, 14 attempts are made from 13 different hosts, with only 70-46-140-187.orl.fdn.com trying more than once. Then thirteen attempts are made for the amanda user, from 13 other hosts. The pattern repeats again for users amavis, apache, at, and goes on with others, apparently trying users in an alphabetic sequence.

Phase 2: Not your run of the mill screwup, the data say
Repeated login attempts for non-existing users are nothing new (in fact the bruteforce avoidance section is one of the more popular parts of the PF tutorial), but I was a bit surprised to see the attempts actually reaching this machine, which is on a local network behind a PF gateway with a configuration that is in fact closely related to the one in the tutorial (and the book for that matter). Then looking at the log entries, I noticed a few more things: The attempts are never less than a minute apart, and the attempts from a single host are separated by much longer intervals. The full data set I extracted from the point I started noticing those anomalies sum up to these figures can be found here, in case you want to look at it and draw you own conclusions

Some one-liners give us illustrative numbers:

peter@thingy:~$ wc -l slowbrutes.txt
16727 slowbrutes.txt
That is, over this period there were 16727 failed ssh login attempts at this host. A large number for this particular machine, but not enough to raise eyebrows by itself at larger or busier sites.

More than sixteen thousand attempts, but for how many invalid user names?

peter@thingy:~$ grep illegal slowbrutes.txt | awk '{print $13}' | sort -u | wc -l
2962
peter@thingy:~$ grep illegal slowbrutes.txt | awk '{print $15}' | sort -u | wc -l
671
That is, approaching three thousand unlucky guesses, coming from 671 different hosts.

How many valid user names did they stumble upon?

peter@thingy:~$ grep -v illegal slowbrutes.txt | awk '{print $11}' | sort -u | wc -l
2
A grand total of two, one of them the rather obvious root, for a total of

peter@thingy:~$ grep -vc illegal slowbrutes.txt
1698
1698 attempts, coming from

peter@thingy:~$ grep -v illegal slowbrutes.txt | awk '{print $13}' | sort -u | wc -l
566
566 different hosts.

The patterns that emerge from the data, with the alphabetical ordering and apparent coordination, point to a botnet herder trying out new methods. Intrusion detection systems and adaptive firewalls are generally tuned to detecting things like large numbers of simultaneous connecions or a high rate of new connections from a host. Distributing the task of bruteforcing passwords to several hosts could seem like an inspired way to come in under the radar wherever relatively smart systems are in place. Setting the herd to attempt at a low frequency would likely mean that those failed attempts simply drown in the noise at higher volume sites, and will not be noticed.

Phase 3: Are you one of their guinea pigs, too?
There are indications that the method has not been quite perfected yet. At the start of this run, the bots would make at least ten attempts before moving on down the alphabet. Now it seems enough bots have been taken out of circulation that the typical number of attempts per user name is closer to three, with some tried only once:

Dec 2 11:45:59 rosalita sshd[55775]: error: PAM: authentication error for illegal user heaven from cpe001217e403b3-cm000f9fa6157c.cpe.net.cable.rogers.com
Dec 2 11:48:16 rosalita sshd[55778]: error: PAM: authentication error for illegal user heaven from 90.190.96.46
Dec 2 11:50:39 rosalita sshd[55791]: error: PAM: authentication error for illegal user heaven from static-71-117-126-102.snloca.dsl-w.verizon.net
Dec 2 11:55:26 rosalita sshd[55811]: error: PAM: authentication error for illegal user heavynne from dsl-217-155-184-54.zen.co.uk
Dec 2 11:57:57 rosalita sshd[55814]: error: PAM: authentication error for illegal user heavynne from pd907ee1e.dip0.t-ipconnect.de
Dec 2 12:00:20 rosalita sshd[55836]: error: PAM: authentication error for illegal user heba from 201-26-172-213.dial-up.telesp.net.br
Dec 2 12:07:37 rosalita sshd[55879]: error: PAM: authentication error for illegal user hector from 75.145.16.83
Dec 2 12:09:58 rosalita sshd[55882]: error: PAM: authentication error for illegal user hector from ppp-69-217-30-214.dsl.applwi.ameritech.net
Dec 2 12:12:33 rosalita sshd[55901]: error: PAM: authentication error for illegal user hector from 75-49-251-71.lightspeed.snjsca.sbcglobal.net
Dec 2 12:14:51 rosalita sshd[55905]: error: PAM: authentication error for illegal user hedda from 201.218.231.142
Dec 2 12:17:21 rosalita sshd[55911]: error: PAM: authentication error for illegal user hedda from 75.147.27.85
Dec 2 12:19:48 rosalita sshd[55914]: error: PAM: authentication error for illegal user hedda from 203.70.179.113
From where I'm sitting it's hard to tell whether the lower number of attempts means that the machines have cleaned up by their legal owners or whether they have simply taken out of rotation by their herders. Even with the initial 14 attempts per user name the chance of actually finding a valid combination of user names and passwords would be slim but not non-existent, but decreasing the number of attempts per time unit will necessarily make the chance of eventually finding a valid pair even smaller.

Apparently I'm not the only one seeing the slow brutes, as this post to openbsd-misc indicates. The sensible countermeasure could be to disallow shh password logins and allow only key logins, probably easier to set up and enforce than network-level measures. With the slow rate of attempts and the relatively large number of hosts involved, the undesirable traffic here is relatively hard to distinguish automatically from innocent errors unless you make have any attempt to log in with an invalid user name a sufficent reason for blocking traffic from that host.

Phase N: The shape of things to come
In the longer term view, this may very well be the shape of botnets to come. With a large enough pool of compromised hosts under their control, future botnet herders can afford to organize their activity so any one host only participates in undesirable activity at intervals long enough that malware detectors do not trigger (and thinking further ahead, if the world ever does go IPv6 wholesale and you can expect any one network interface to have dozens of IP addresses, think again how much more interesting detecting botnets becomes).

Antiware vendors will likely put their spin on this too when their marketing departments start noticing columns (Hey! It's Linux they're targeting!), but then as regular readers know, the more productive approach is always to reduce malware masters' target area by using systems that are less vulnerable because they have been extensively audited and whose makers are unafraid to make source code available for public inspection and experimentation.

---

As people who ran into me at the recent PF tutorial in London or at OpenCON will already know, have I joined FreeCode, the Norwegian free software consultancy. We expect to keep doing fun and useful things with free software for customers and friends, and some of it may be interesting enough to be the topics of future columns.


Note: A Better Data Source Is Available
Update 2013-06-09: For a faster and more convenient way to download the data referenced here, please see my BSDCan 2013 presentation The Hail Mary Cloud And The Lessons Learned which summarizes this series of articles and provides links to all the data. The links in the presentation point to a copy stored at NUUG's server, which connects to the world through a significantly fatter pipe than BSDly.net has.