by Corey Nachreiner, CISSP, Network Security Analyst, WatchGuard Technologies
[Editor's Note: This article supplements the list of attacks shown in Part 2 of the video series, Malware Analysis: Botnets. "Malware Analysis: Botnets, Part 2" shows a small subset of botnet attacks in action. This article fills out that subset with more attacks commonly found in a bot herder's arsenal. LiveSecurity subscribers can find the videos, free of charge, on our Video Tutorials page. --Scott]
You’ll often hear botnets described as a “hacker’s Swiss army knife.” Just as a Swiss army knife can come with a crazy variety of blades, scissors, and screwdrivers, bots come with numerous exploits and commands that allow bot herders to launch many different types of attacks.
Since coding up a bot client takes time and skill, most attackers buy bot code in the online underground. Popular malicious bots include Phatbot, Agobot, and the one shown in our video, Rxbot. These bot clients use modular code, so if a bot herder doesn’t love the array of commands his bot offers, he simply adds new ones. For examples, read on.
What pairs better than zombies and spam?
Bot herders commonly leverage their bots as huge spam relays. How huge? According to a recent study by Commtouch, 87% of all email sent over the Internet during 2006 was spam. This e-junk generated up to 1700 terabytes (1,700,000,000 megabytes) of Internet traffic every day. Botnets generated 85% of that spam, a tidal wave of unwanted mail.
Most bot code comes with at least a few commands to make spamming easier. Some bots are even optimized specifically for spamming. A bot herder using Phatbot can issue the command harvest.emails to collect every email address on a victim’s computer. If a Phatbot herder’s botnet consists of thousands of victim machines, he could quickly and easily create gi-normous email lists to later spam.
Agobot is customized for spamming. It even includes its own SMTP engine so that it can spam directly. Its email spamming commands allow an Agobot herder to tell each of his victim’s computers to:
- Download a list of email addresses to spam
- Download a template email message to send out
- Start sending out messages using many different email threads simultaneously
- Start and stop spamming when instructed to.
The bot in our video, Rxbot, is not considered a spamming bot. However, even it contains an elementary command that allows a bot herder to send an email from all his zombie victims.
I’m hiding behind my SOCKS
Many bots include a SOCKS server. SOCKS (an abbreviation for sockets) is a networking protocol designed to pass TCP traffic through a proxy server. In other words, if a client wanted to visit www.google.com using SOCKS, the client would send its request to a SOCKS server instead of to Google directly. The SOCKS server forwards that request to Google and returns the response to the client. However, to Google it looks as though the request came from the SOCKS server, not the actual client.
Bot herders love to use the SOCKS proxy to spam. A bot master simply enables the SOCKS proxy on one of his bots, then redirects his SOCKS-compatible, mass emailing program to the IP address of that bot. This causes the email program to send email using that bot as a relay. If an anti-spam program blacklists the bot’s IP address, the herder activates the SOCKS proxy on another bot, and his spam seems to originate from a new, clean IP address.
Furthermore, the bot herder can use a SOCKS proxy to anonymize just about any network traffic. And in Rxbot, for instance, activating the SOCKS proxy is simple: one six-letter command initiates all those anonymizing benefits.
Some bots have a Man-in-the-Middle
Bots also help herders launch Man-in-the-Middle (MitM) attacks. Most bots come with commands that allow their creators to redirect network traffic any way they like. For instance, a bot herder could tell a bot to redirect all its web traffic to his computer. Then, every time the unwitting victim (whose machine is hosting that bot) browses the Web, the attacker sees the traffic before forwarding it to its intended destination. This is one way bot masters capture sensitive information or steal login credentials.
Rxbot comes with the .redirect command. Herders can use this command to forward the network traffic destined for any TCP port, to any IP address they choose. Phatbot comes with additional redirect commands that allow it to forward GRE traffic, the special protocol used in establishing PPTP VPN connections. These examples merely hint at what a bot herder can accomplish with redirects.
Click Fraud and Poll Manipulation
Nowadays, the lure of illegal easy money motivates most bot herders. Our video shows how crooks can force their bots to click on revenue-generating Google ad words. As another example, Rxbot has a simple-yet-effective .visit command. If you send your bots this command, followed by a URL, they silently visit that URL. Here, silently is a technical term meaning the bot victim will not see her computer visit the URL. The visit happens in the background, without any web browser involvement. So, imagine you have 100,000 bots. With one command you could easily force all those bots to visit an online poll, vote, or game. If you wanted ToneDeaf UglyDork to win American Idol, you could command all your bots to visit the American Idol voting page and submit a vote. Since every vote would come from a different IP address, the results would look legitimate. And if the flaws in American e-voting aren’t fixed before 2008, bots just might elect ToneDeaf UglyDork as President, too.
Spam + IM = SPIM
Many IRC bots today have Instant Messenger (IM) and Peer-to-Peer (P2P) components in their attack arsenal. For instance, some bots allow you to send spam to IM channels (nicknamed SPIM ). Attackers commonly send malicious files or URLs to IM users, hoping to infect them with malware. Some bots incorporate commands that allow the bot herder to send these types of IM messages to his bots’ IM buddies. If those buddies then visit the URL or execute an attached file, they get infected with the herder’s bot and become minions in his botnet.
Some bots offer similar commands that help them spread via P2P applications. For instance, Agobot spreads by placing copies of itself in the share directories used by many popular P2P programs such as Kazaa and Limewire. The bot gives its file an enticing name, such as the title of a movie still in theaters. When someone downloads and runs this malicious trojan, their computer becomes another zombie.
Is it just me, or does it smell like bots in here?
In the video, we mentioned that many bots come with packet sniffers. Packet sniffers allow a bot master to see all of the network traffic that passes by his bots, and sometimes all the traffic that passes within the bot victim’s network as well. Attackers can learn a lot by sniffing a network. For instance, a bot herder might capture cleartext logins or see web cookies. They could even passively enumerate your infected network.
Agobot comes with some very advanced packet sniffing capabilities. Rather than sniffing and reporting every single packet, which creates volumes of junk for the herder to parse, Agobot allows a herder to sniff for specific strings or types of traffic. For example, you can command Agobot to capture all the web cookies it sees passing over a network. You can also specifically tell it to only sniff FTP, or IRC logins. In short, if something passes over a network in clear text, Agobot’s sniffing can pinpoint it.
Stay as sharp as the crooks
In our video and this article, we’ve listed the most common “Swiss Army blades” used in bots today. Since botnets are evolving fast, bots could have all-new blades tomorrow. For now, you can protect yourself best by understanding the threat — and following the defense measures we outline in “Malware Analysis: Botnets, Part 3.” Look for it on our Video Tutorials page beginning 17 October, 2007. #
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