Srizbi is back

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Update: The new Estonian company that hosted the command & control server, Starline Web Services, was shut down. The domain name chase continues !

The Srizbi botnet is back online after being shut down by the closure of the criminal hosting company McColo Corp two weeks ago. Srizbi’s command and controls servers, now moved to an Estonian hosting provider, took back control of the botnet[1] in the last days.

The Srizbi Botnet

The Srizbi botnet is mostly a spam generating botnet. According to security firm FireEye, there are 50 variants of the bot, which controls altogether around 500 000 zombies across the world[2]. The most virulent forms of Srizbi are said to control around 50 000 bots.

The Srizbi botnet had a backup procedure in case its C&C servers went down, that is why it got back online very fast. Included in the bot, is a procedure that generates domain names[3] and tries to contact it to see if the C&C is available. Therefore the owners, knowing the random-generating domain name algorithm of the botnet, only had to register one or more of the domain names that will be generated by the bots and install their new control and command server on a machine registered a valid domain name. That is enough for bots to download a new version, pointing to a new address for the botnet. To explain it using pseudo-code, it would look something like this:

More information can be found about the random name generation algorithm at FireEye[4]. Interesting enough, the algorithm is based on date to generate a new set of possible domains names by period. FireEye had successfully discovered this function after McColo closed, but due to financial constraint, they could not register all the domain names that the bot generated. That would have implied to register more than 450 domains each week…

We have registered a couple hundred domains,” Fengmin Gong, chief security content officer at FireEye Inc., “but we made the decision that we cannot afford to spend so much money to keep registering so many [domain] names.[5]

Communications intercepted between a Srizbi bot and its Command and Control Server
Communications intercepted between a Srizbi bot and its Command and Control Server

According to the Symantec Srizbi webpage[6], the worm creates windbg48.sys and another randomly named .SYS file in the %SYSTEM% folder. It then registers the wingdbg48.sys as a driver by inserting the hidden HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\windbg48 key into the Windows’ Registry. Srizbi hides those keys by running in Kernel mode and hooking the ZwOpenKey and ZwEnumerateKey kernel functions among others. It might also try to block access to the registry. A tool is available in order to access the registry anyway.

It will also hide its files by hooking the NTFS file system driver. As if it was not enough, it will also modify the TCP/IP network drivers to bypass Firewalls and Intrusion Detection systems. It will also work in Safe Mode.

For those who wish to go deeper, Windows has two levels of execution: user mode and kernel mode. Usually applications run in user mode, which protects the kernel from applications so they won’t mess up the system. Kernel mode is a privilege mode where services and drivers have access to system resources such as the processor but also the memory… Hooking kernel functions is done by redirecting calls made to the kernel to a custom function. There are a couple of ways to do that in kernel mode, and one of them is to alter the System Service Descriptor Table, which is a table that maps every kernel function to an address in memory. By modifying this table to the address of your custom function, you could hook the kernel. This however would be easily detected by any anti-virus.

Another way is to insert an unconditional jump instruction into the kernel function by modifying the function directly in memory. The advantage of this method is that it’s much harder to detect, and can reproduce the same functionality of the hooked function. This is called inline function hooking.

This why this Trojan can also work in Safe Mode. I don’t know if this particular Trojan uses inline function hooking, but rootkits that uses this kind of hooking are quite hard and dangerous to remove.

Return of Srizbi

When McColo Corp. closed two weeks ago following and investigation by the Washington Post’s Security Fix, it made the news across the Internet as this hosting company was considered responsible for around 75 percent of all the spam sent across the web. Although many rejoiced, including me, at the sudden drop of spam as soon as McColo was turn off[7], everyone knew it was only temporary before the cyber criminals would found another hosting company.

Few knew that this random domain name generating routine was coded to connect to another C&C server though. As soon as it came back online, the first command it received was for a Russian spam campaign. By generating domain names such as yrytdyip.com, auaopagr.com, qpqduqud.com or ydywryfu.com, it was unthinkable for FireEye to register every possibility generated by Srizbi. It is becoming harder and harder to fight botnets on a technical basic. Fortunately, the economic fight could maybe put an end to spam, as mentioned in this Ars Technica article:

“… it suggests that spammers may be extremely sensitive to costs-more so than was previously believed. Even a small increase in the cost of sending an e-mail, they postulate, could have significant ramifications for the botnet industry, and might slow the rate at which it grows or put some spam operations out of business altogether.[8]

The Rustock, Cutwail and Asprox botnets are also making a come back[9], provoking a new surge in spam in the last few days, but not quite yet at the same level of the pre-McColo era.

See also:

Windows Rootkits of 2005, Part One“, James Butler, Sherri Sparks, Security Focus, November 4, 2005, http://www.securityfocus.com/infocus/1850, (accessed on November 27, 2008)

Fallback C&C channels“, Alex Lanstein, Atif Mushtaq, Julia Wolf, and Todd Rosenberry, FireEye, November 16, 2008,  http://blog.fireeye.com/research/2008/11/fallback-cc-channels-part-deux.html#more (accessed on November 27, 2008)


[1] “Massive botnet returns from the dead, starts spamming”, Gregg Keizer, ComputerWorld, November 26, 2008, http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9121678 (accessed on November 27, 2008)

[2] “Srizbi Botnet Re-Emerges Despite Security Firm’s Efforts”, Brian Krebs, Washington Post – Security Fix, November 26, 2008, http://voices.washingtonpost.com/securityfix/2008/11/srizbi_botnet_re-emerges_despi.html?hpid=news-col-blogs (accessed on November 27, 2008)

[3] “Technical details of Srizbi’s domain generation algorithm”, Julia Wolf, November 25, 2008, http://blog.fireeye.com/research/2008/11/technical-details-of-srizbis-domain-generation-algorithm.html (accessed on November 27, 2008)

[4] Ibid.

[5] “Massive botnet returns from the dead, starts spamming”, Gregg Keizer, ComputerWorld, November 26, 2008, http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9121678 (accessed on November 27, 2008)

[6] “Trojan.Srizbi”, Kaoru Hayashi, Symantec, July 23, 2007, http://www.symantec.com/security_response/writeup.jsp?docid=2007-062007-0946-99&tabid=2 (accessed on November 27, 2008)

[7] “Spam plummets after Calif. hosting service shuttered”, Gregg Keizer, ComputerWorld Security, http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9119963 (accessed on November 27, 2008)

[8] “Study: Storm botnet brought in daily profits of up to $9,500”, Joel Hruska, Ars Technica, November 10, 2008, http://arstechnica.com/news.ars/post/20081110-study-storm-botnet-brought-in-daily-profits-of-up-to-9500.html (accessed on November 27, 2008)

[9] “Srizbi botnet active again”, Jeremy Kirk, November 27, 2008, http://www.itworldcanada.com/a/Departmental-and-End-User-Computing/7167ba6c-1cd2-4c54-9338-95a63bea47fa.html (accessed on November 27, 2008)

How do Spammers Make Money?

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A very interesting article on the BBC discussed on how to spammers actually earn money with their system.

Many of us might have asked themselves the question on “why do spammers still sends their e-mails?”, or “how to they make money?” After all, most of computer users know about spam by now. Well it appears that even if spammers gets only one answer for 12.5 million e-mail sent[1], that’s all they need to make the big bucks. That’s what a team from the International Computer Science Institute found out in their paper “Spamalytics: An Empirical Analysis of Spam Marketing Conversion“.

The researchers hijacked a part of the Storm botnet, which used to be one of the biggest botnet around, and rewrote a part of the command and control module of the bot. In order to measure the success of the spam campaign, the team set up two websites, one being a fake Canadian pharmacy and another was postcard website, used to make the user download malware.

Overall, the computer scientists spawn 8 proxies and 75 869 worker bots[2]. They sent 469 million of spam emails, trying to convince the recipients to buy products from the fake online pharmacy. They also made sure to distinguish the visitors on their website by identifying crawlers and honey clients from genuine clients.

From the 350 million spams sent for the pharmacy website, for a period of 26 days, only 28 people went to visit the purchase page of the fake website[3].

Location of the victims that visited the postcard website (white/gray dots) and the 28 victims that went to the purchase page of the pharmacy.

According to the report:

Under the assumption that our measurements are representative over time (an admittedly dangerous assumption when dealing with such small samples), we can extrapolate that, were it sent continuously at the same rate, Storm-generated pharmaceutical spam would produce roughly 3.5 million dollars of revenue in a year. This number could be even higher if spam-advertised pharmacies experience repeat business. A bit less than “millions of dollars every day”, but certainly a healthy enterprise[5].

The report can be found here.


[1] “Study shows how spammers cash in”, BBC News, November 10, 2008, http://news.bbc.co.uk/2/hi/technology/7719281.stm (accessed on November 10, 2008)

[2]Spamalytics: An Empirical Analysis of Spam Marketing Conversion“, Chris Kanich, Christian Kreibich, Kirill Levchenko, Brandon Enright, Geoffrey M. Voelker, Vern Paxson, Stefan Savage, International Computer Science Institute, 2008, p.6

[3] Ibid. p.11

[4] Ibid. p.9

[5] Ibid. p.11

Malware Authors Loves Obama Too

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The Register reports that malware creators are already using Mr. Obama’s popularity to distribute the Papras Trojan using spam, social engineering and Google Ads[1].

Users usually receive an email from what seems a legitimate news sources such as CNN and BBC, inviting users to see the speech of Barack Obama on their website. The content of the email is the following[2]:

Barack Obama Elected 44th President of United States

Barack Obama, unknown to most Americans just four years ago, will become the 44th president and the first African-American president of the United States.
Watch His amazing speech at November 5!

Proceed to the election results news page>>

2008 American Government Official Website
This site delivers information about current U.S. Foreign policy and about American life and culture.

And senders are usually:

  • news@cnn.com
    news@usatoday.com
    news@online.com
    news@c18-ss-1-lb.cnet.com
    news@president.com
    news@unitedstates.com
    news@bbc.com

The email contains a link to a fake website, which prompts the users to update their Flash player in order to see the speech. Of course, the update is actually a Trojan.

Screen shots of the email and fake website, from F-Secure[3]:

 

Papras is an information stealing Trojan, trying to get a hold of logins and passwords among others. This Trojan is detected by only 14 of the 36 major anti-virus programs.


[1] “Obama-themed malware mauls world+dog”, Dan Goodin, The Register, November 5, 2008, http://www.theregister.co.uk/2008/11/05/obama_malware_attacks/ (accessed November 6, 2008)

[2] “Computer Virus masquerades as Obama Acceptance Speech Video”, Gary Warner, CyberCrime & Doing Time, November 5, 2008, http://garwarner.blogspot.com/2008/11/computer-virus-masquerades-as-obama.html (accessed on November 6, 2008)

[3] “US Presidential Malware”, F-Secure, November 5, 2008, http://www.f-secure.com/weblog/archives/00001530.html (accessed on November 6, 2008)