The following is an excerpt from the book Virtual Honeypots: From Botnet Tracking to Intrusion Detection
. In this section of Chapter 11:Tracking Botnets (.pdf), authors Niels Provos and Thorsten Holz explain how virtual honeypots can be used in the real world to investigate botnets and their behavior.
Something that is interesting, but rarely seen is botnet owners discussing issues in their bot channel. We observed several of those talks and learned more about their social life this way. The bot-herders often discuss issues related to botnets but also talk about other computer crime–related things or simply talk about what they do.
Our observations showed that often botnets are run by young males with surprisingly limited programming skills. These people often achieve a good spread of their bots, but their actions are more or less harmless. Nevertheless, we also observed some more advanced attackers, but these persons joined the control channel only occasionally. They use only one-character nicks, issue a command, and leave. The updates of the bots they run are very professional. Probably these people use the botnets for commercial usage and sell the services. More and more attackers use their botnets for financial gain. For example, by installing browser extensions, they are able to track/fool websurfers, click pop-ups in an automated way, or post adware as presented in the previous section. A small percentage of bot-herders seem highly skilled. They strip down the software used to run the C&C server to a non-RFC-compliant daemon, not even allowing standard IRC clients to connect.
Moreover, the data we captured while observing the botnets show that these control networks are used for more than just DDoS attacks. Possible usages of botnets can be categorized as listed here. And since a botnet is nothing more than a tool, there are most likely other potential uses that we have not listed.
Spamming: Some bots offer the possibility to open a SOCKS v4/v5 proxy —a generic proxy protocol for TCP/IP-based networking applications — on a compromised machine. After enabling the SOCKS proxy, this machine can then be used for nefarious tasks such as sending bulk e-mail (spam) or phishing mails. With the help of a botnet and thousands of bots, an attacker is able to send massive amounts of spam. Some bots also implement a special function to harvest e-mail addresses from the victims.
In addition, this can, of course, also be used to send phishing mails, since phishing is a special case of spam. Also increasing is so-called stock spam: advertising of stocks in spam e-mails. In a study we could show that stock spam indeed influences financial markets.
Spreading new malware: In many cases, botnets are used to spread new bots. This is very easy, since all bots implement mechanisms to download and execute a file via HTTP or FTP. But spreading an e-mail virus using a botnet is a very nice idea, too. A botnet with 10,000 hosts that acts as the start base for the mail virus allows very fast spreading and thus causes more harm. The Witty worm, which attacked the ICQ protocol parsing implementation in Internet Security Systems (ISS) products, is suspected to have been initially launched by a botnet because some of the attacking hosts were not running any ISS services.
Installing advertisement addons and Browser Helper Objects (BHOs): Botnets can also be used to gain financial advantages. This works by setting up a fake website with some advertisements. The operator of this website negotiates a deal with some hosting companies that pay for clicks on advertisements. With the help of a botnet, these clicks can be automated so that instantly a few thousand bots click on the pop-ups. This process can be further enhanced if the bot hijacks the start-page of a compromised machine so that the clicks are executed each time the victim uses the browser.
Google AdSense abuse: A similar abuse is also possible with Google's AdSense program. AdSense offers companies the possibility to display Google advertisements on their own website and earn money this way. The company earns money due to clicks on these ads — for example, per 10,000 clicks in one month. An attacker can abuse this program by leveraging his botnet to click on these advertisements in an automated fashion and thus artificially increment the click counter. This kind of usage for botnets is relatively uncommon but not a bad idea from an attacker's perspective.
Attacking IRC networks:
Botnets are also used for DDoS attacks against IRC networks. Popular among attackers is especially the so-called clone attack. In this kind of attack, the controller orders each bot to connect a large number of clones to the victim's IRC network. The victim is overwhelmed by service requests from thousands of (cloned) bots.
Manipulating online polls/games: Online polls/games are getting more and more attention, and it is rather easy to manipulate them with botnets. Since every bot has a distinct IP address, every vote will have the same credibility as a vote cast by a real person. Online games can be manipulated in a similar way.
Currently we are aware of bots being used that way, and there is a chance that this will get more important in the future.
Sniffing traffic: Bots can also use a packet sniffer to watch for interesting clear-text data passing by a compromised machine. The sniffers are mostly used to retrieve sensitive information like usernames and passwords.
But the sniffed data can also contain other interesting information: If a machine is compromised more than once and is also a member of more than one botnet, the packet sniffing allows one to gather the key information of the other botnet. Thus, it is possible to "steal" another botnet.
Keylogging: If the compromised machine uses encrypted communication channels (e.g., HTTPS or POP3S), then just sniffing the network packets on the victim's computer is useless, since the appropriate key to decrypt the packets is missing. But most bots also implement functions to log keystrokes. With the help of a keylogger, it is very easy for an attacker to retrieve sensitive information.
An implemented filtering mechanism (e.g., "I am only interested in key sequences near the keyword 'paypal.com'") further helps in stealing secret data.
Harvesting of information: Sometimes we can also observe the harvesting of information from all compromised machines. With the help of special commands, the operator of the botnet can request a list of sensitive information from all bots.
With our method we can shut down the root cause of all of these types of nuisances, and hence the preceding methodology cannot only be used to combat DDoS.
To find out how the authors were able to make such observations about botnet behavior, read all of Chapter 11: Tracking Botnets (.pdf)
Reproduced from the book Virtual Honeypots: From Botnet Tracking to Intrusion Detection
Copyright , Addison Wesley Professional. Reproduced by permission of Pearson Education, Inc., 800 East 96th Street, Indianapolis, IN 46240. Written permission from Pearson Education, Inc. is required for all other users.
This was last published in October 2007
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