Backdoor:Win32/Rustock is a rootkit-enabled proxy trojan used to send large volumes of spam from infected computers. When Backdoor:Win32/Rustock is first run, the user mode installer checks to see if the global atom {DC5E72A0-6D41-47e4-C56D-024587F4523B} exists, the presence of which signifies that another copy of Backdoor:Win32/Rustock.gen!A is already active on the system. If another copy of the trojan exists, the installer portion of Backdoor:Win32/Rustock exits. If it does not already exist, Backdoor:Win32/Rustock tries to install a kernel mode driver by attaching itself as an alternate data stream (ADS) to the Windows system folder, for example, %windir%>\System32:lzx32.sys (ADS is supported on all NT-based operating systems). On systems that do not support ADS, Backdoor:Win32/Rustock drops a file to the <system> folder, registers that file as a service and starts the service when installation is complete. The driver is installed with the following properties:
Type = 1
Start = 1
ImagePath = c:\windows\system32\lzx32.sys or system32:lzx32.sys
DesiredAccess = 10h
DisplayName = Win23 lzx files loader
ServiceName = pe386 or lzx32
Backdoor:Win32/Rustock injects its code into any user mode processes named "explorer". This can enable Backdoor:Win32/Rustock to bypass policy restrictions and access the Internet. Backdoor:Win32/Rustock gathers system information and collects email addresses from a wide range of file types found on the infected system and attempts to send the collected data via HTTP to 208.66.195.248.
Backdoor:Win32/Rustock may also download an ICQ chat program. Additionally, in an attempt to bypass Bayesian-type spam filters, Backdoor:Win32/Rustock connects to various pre-defined URLs, querying and collecting text from those sites which it uses in the plain text alternate section of email it composes.
Kernel Mode Rootkit
The kernel mode rootkit driver component of Backdoor:Win32/Rustock hides registry keys, files, TCP ports and memory objects. It also hides itself from the applications which contain the following strings: RootkitReveller, BlackLight, Rkdetector, Gmer, Endoscope, DarkSpy, and Anti-rootkit. The driver also looks for "Rustock" and "rootkit" strings within processes and, if found, changes its behavior to avoid detection. In addition, the kernel mode driver creates the global atom {DC5E72A0-6D41-47e4-C56D-024587F4523B} to alert the user mode installer that this driver is already installed.
Backdoor:Win32/Rustock alters the behavior of the following APIs: ZwOpenKey, ZwEnumerateKey, ZwQueryKey, ZwCreateKey, ZwSaveKey, ZwDeviceIoCOntrolFile, ZeInitializeRegistry, ZWQuerySystemInformation, ZwTerminateProcess, and filters these APIs' output if the strings pe386 or lzx32 are detected. It also intercepts and processes IRP_MJ_CREATE and IRP_MJ_QUERY_INFORMATION, and hooks the following drivers in memory: tcpip.sys, wanarp.sys, and ndis.sys.
Take the following steps to help prevent infection on your computer:
-
Enable a firewall on your computer.
-
Get the latest computer updates for all your installed software.
-
Use up-to-date antivirus software.
-
Limit user privileges on the computer.
-
Use caution when opening attachments and accepting file transfers.
-
Use caution when clicking on links to Web pages.
-
Avoid downloading pirated software.
-
Protect yourself against social engineering attacks.
-
Use strong passwords.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor Web sites.
You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
Use up-to-date antivirus software
Limit user privileges on the computer
Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.
You can configure UAC in your computer to meet your preferences:
Use caution when opening attachments and accepting file transfers
Exercise caution with e-mail and attachments received from unknown sources, or received unexpectedly from known sources. Use extreme caution when accepting file transfers from known or unknown sources.
Use caution when clicking on links to Web pages
Exercise caution with links to Web pages that you receive from unknown sources, especially if the links are to a Web page that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a Web page with harmful content.
Avoid downloading pirated software
Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see '
The risks of obtaining and using pirated software'.
Protect yourself from social engineering attacks
While attackers may attempt to exploit vulnerabilities in hardware or software to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted computer. For more information, see '
What is social engineering?'.
Use strong passwords
Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least 8 characters, and combines letters, numbers, and symbols. For more information, see
http://www.microsoft.com/protect/yourself/password/create.mspx.
