1. Symantec/
  2. Security Response/
  3. Backdoor.Rustock.B


Risk Level 1: Very Low

July 5, 2006
February 13, 2007 12:57:18 PM
Also Known As:
Spam-Mailbot.c [McAfee]
Trojan Horse
Systems Affected:

When Backdoor.Rustock.B is executed, it performs the following actions:
  1. Creates the following hidden alternate data streams:


    Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows or C:\Winnt.

  2. Creates a hidden device service with the following characteristics:

    Display name: Win23 lzx files loader
    ImagePath: %Windir%\System32:lzx32.sys

  3. Creates the following registry subkey associated to the hidden device service:


  4. Uses advanced Rootkit techniques to hide the registry subkeys it creates and to prevent access to the alternate data streams file. It hooks MSR_SYSENTER code and patches several area of Windows Kernel to change the functioning of the following APIs:

    • ZwOpenKey
    • ZwEnumerateKey
    • ZwQueryKey
    • ZwCreateKey
    • ZwSaveKey
    • ZwDeviceIoControlFile
    • ZwQuerySystemInformation
    • ZwInitializeRegistry

  5. Scans Windows Kernel image in memory for the following string and replaces it with a malicious code that executes the Rootkit functions:


  6. Attempts to hide itself from applications that contain one of the following strings:

    • RootkitRevealer
    • BlackLight
    • Rkdetector
    • gmer.exe
    • endoscope.EXE
    • DarkSpy
    • Anti-Rootkit

  7. Alters the correct functioning of the following system modules used for network communications to bypass firewalls and to perform network packet manipulations:

    • tcpip.sys
    • wanarp.ss
    • ndis.sys

  8. May create the following temporary file where it stores its data:


    Note: %Temp% is a variable that refers to the Windows temporary folder. By default, this is C:\Windows\TEMP (Windows 95/98/Me/XP) or C:\WINNT\Temp (Windows NT/2000).

  9. May also download the following ICQ program:


  10. May hijack web navigation and redirect HTTP traffic. It also attempts to post the following HTTP query on Google search engine:


    Where [KEYWORDS] is a random chosen keyword as in the following examples:

    • [http://]ww.google.com/search?hl=en&q=news%2Blove
    • [http://]www.google.com/search?hl=en&q=data%2Bgames%2Bfree
    • [http://]www.google.com/search?hl=en&q=enter

  11. May contact the following remote hosts:


  12. Acts as a covert proxy on the compromised computer.

  13. May also be used to send spam emails through the computer.


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Elia Florio
Summary| Technical Details| Removal

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