W32.Waledac

1. Prevention and avoidance
1.1 User behavior and precautions
1.2 Patch operating system and software
2. Infection method
2.1 Email
2.2 Fake websites
2.3 Bundled with other threats
3. Functionality
3.1 System modifications
3.2 Network activity
3.3 Spam
3.4 Downloading further risks
3.5 Infostealer
3.6 Botnet topology
4. Additional information



1. PREVENTION AND AVOIDANCE
The following actions can be taken to avoid or minimize the risk from this threat.


1.1 User behavior and precautions
W32.Waledac relies heavily on social engineering in order to infect computers. The spam email campaigns used by attackers attempt to trick the user by referencing the latest news stories, seasonal holidays, or any number of other ruses.

Users should use caution when clicking links in such emails. Basic checks such as hovering with the mouse pointer over each link will normally show where the link leads to. Users can also check online website rating services such as safeweb.norton.com to see if the site is deemed safe to visit.


1.2 Patch operating system and software
The attackers behind this threat have been known to utilize exploit packs in order to craft Web pages to exploit vulnerable computers and infect them with W32.Waledac. Users are advised to ensure that their operating systems and any installed software are fully patched, and that antivirus and firewall software is up to date and operational. Users are recommended to turn on automatic updates if available so that their computers can receive the latest patches and updates when they are made available.



2. INFECTION METHOD
This threat is known to infect computers through a number of methods. We will examine each of these methods in more detail.


2.1 Email
The people behind Waledac periodically utilize spam campaigns with subject lines and message bodies based on the latest search terms or topical news stories. Topics have ranged from Christmas wishes, the 2009 US Presidential race, Valentine’s Day, the 4th of July, and even spying on your partner. These emails usually contain a link, often pointing to a Waledac binary hosted on a malicious website. In other cases they are brought to a fake website that continues the ruse and exploits vulnerable computers, installing its malicious software on the computer.


2.2 Fake websites
The fake websites designed by the people behind Waledac work in a variety of ways. They may simply attempt driveby download-style attacks, focusing on exploits for known (or sometimes 0-day) vulnerabilities. In other cases, the Waledac authors create fairly elaborate websites, attempting to add an air of legitimacy in order to trick the user into installing the threat, such as the following example:




2.3 Bundled with other threats
Waledac doesn’t just spread itself. It has made appearances with a surprising number of other threats. We have seen threats such as Trojan.Peacomm, W32.Downadup, and Trojan.Bredolab, among others, working in tandem with Waledac. The connection between these threats and Waledac is unknown, but is most likely a testament to its functionality once a computer has been compromised.



3. FUNCTIONALITY


3.1 System modifications
The install files for Waledac vary widely, where each spam campaign or hosting website changes the file names, depending on the situation. There are even cases where Waledac utilizes server-side polymorphism, where the executables hosted on the malicious domains are repacked and encrypted at fairly regular intervals. This is no doubt an attempt to evade file-based detections when the threat initially arrives on a computer.

One consistent item in the installation of Waledac is the name of the registry entries that it creates. While the executable file names will vary, a registry entry called “PromoReg” should appear in the following locations:

• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\"PromoReg" = "[PATH TO THREAT]"
• HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\"PromoReg" = "[PATH TO THREAT]"

It will also add its own configuration entries to the registry, hiding them in the “CurrentVersion” subkey. While the values will vary, the entries are as follows:

• HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\"FWDone"
• HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\"LastCommandId"
• HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\"MyID"
• HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\"RList"
  

3.2 Network activity
Waledac utilizes network connections to carry out its primary functions: to spread spam, download other threats, and upload stolen information from the compromised computer. These features are discussed in detail in subsequent sections.

Besides this, Waledac has the ability to download updates of itself, as well as new components that provide further functionality for the threat. One of these “updates” is WinPcap, which is a legitimate application for monitoring network traffic. However, the threat uses it or less-than-benevolent purposes, assisting in its information stealing capabilities.

Waledac attempts to mask much of its downloading activities by hiding binary files within specially crafted .jpg files. These files contain fully executable code within them, which Waledac can then read and execute. However, these files still keep the JPEG functionality intact. If the user opens the file, the .jpg image will display as though there were nothing unusual about the file.


3.3 Spam
The people behind Waledac family of worms seem to be financially motivated. Given this, sending email spam ranks highly on its list of features. The threat sends out vast amounts of email for questionable products and services. These advertisements range from dubious job offers, to pharmaceuticals, to advertisements for online casinos.

In order to help facilitate the spamming feature, Waledac searches predetermined file types after its initial installation. It gathers any email addresses it finds on the compromised computer, adding them to its collection of addresses to send spam to.


3.4 Downloading further risks
We have also observed Waledac downloading other threats on to compromised computers. Some of the particular misleading applications use names such as Spyware Protect 2009, System Security 2009, and MS AntiSpyware 2009.



Given the financial motives of the Waledac authors, it is likely that they receive a cut of any money garnered from the installation of any misleading applications “purchased” after Waledac installs them.


3.5 Infostealer
Waledac will also monitor standard Internet traffic, such as FTP, POP3, SMTP, and HTTP communications, searching for sensitive information such as user names, passwords, IP addresses, and any server information. While it collects this information and sends it to Waledac-controlled servers, it is unclear specifically what is being done with the data from there, though it is likely used to find and control further computers.

3.6 Botnet topology
The botnet that Waledac-infected computers join is comprised of three types of nodes.

• Slave nodes: Perform the various functions of the threat, such as sending spam, installing other threats, and stealing information.
• Relay nodes: Compromised computers with fast internet connections are often used to proxy traffic between slave nodes and the command and control (C&C) servers. The purpose of these nodes is to route the traffic through multiple points, making it more difficult to locate and shut down the C&C servers and the slave nodes.
• C&C servers: These nodes send the commands through the relay nodes and on to the slave nodes, where the commands are performed.

4. ADDITIONAL INFORMATION
Waledac uses a wide array of advanced features to keep it running and carrying out its primary functions. These include a wide array of custom communication protocols, fast-flux DNS networking, and sharing node IP lists.

For a detailed analysis of these advanced features, please see our whitepaper on Waledac.

We have also written a series of blog entries on Waledac, covering other topics relating to the threat.