Backdoor.Rustock.B

SUMMARY

Backdoor.Rustock.B is a back door Trojan horse that allows a compromised computer to be used as a covert proxy. It uses advanced rootkit techniques to hide any files and registry subkeys it creates.

Protection

• Virus Definitions (LiveUpdate™ Daily) July 5, 2006
• Virus Definitions (LiveUpdate™ Weekly) July 5, 2006
• Virus Definitions (Intelligent Updater) July 5, 2006
• Virus Definitions (LiveUpdate™ Plus) July 5, 2006

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Medium
• Payload: Opens a back door on the compromised computer.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Backdoor.Rustock.B is executed, it performs the following actions:

1. Creates the following hidden alternate data streams:
   
   %Windir%System32:lzx32.sys
   
   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:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicespe386
   
   
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:
   
   FATAL_UNHANDLED_HARD_ERROR
   
   
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:
   
   %Temp%[RANDOM].tmp.log
   
   Note: %Temp% is a variable that refers to the Windows temporary folder. By default, this is C:WindowsTEMP (Windows 95/98/Me/XP) or C:WINNTTemp (Windows NT/2000).
   
   
9. May also download the following ICQ program:
   
   [ftp].icq.com/pub/ICQ_Win95_98_NT4/ICQ_5/icq5_setup.exe
   
   
10. May hijack web navigation and redirect HTTP traffic. It also attempts to post the following HTTP query on Google search engine:
    
    [http://]www.google.com/search?hl=en&g=[KEYWORDS]
    
    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:
    
    maila.microsoft.com
    [http://]208.66.194.14/index.php?page=main
    
    
12. Acts as a covert proxy on the compromised computer.
    
    
13. May also be used to send spam emails through the computer.

Recommendations

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

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Disable System Restore (Windows Me/XP).
2. Restart the computer using the Windows Recovery Console
3. Update the virus definitions.
4. Run a full system scan.
5. Delete any values added to the registry.
   

For specific details on each of these steps, read the following instructions.

1. To disable System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

• How to disable or enable Windows Me System Restore
• How to turn off or turn on Windows XP System Restore

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, reenable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article: Antivirus Tools Cannot Clean Infected Files in the _Restore Folder (Article ID: Q263455).

2. To restart the computer using the Windows Recovery Console
To remove this threat it is necessary to restart the computer and run the Windows Recovery Console. For full details on how to do this please read the Microsoft Knowledge Base article, How to install and use the Recovery Console in Windows XP.

1. Insert the Windows XP CD-ROM into the CD-ROM drive.
2. Restart the computer from the CD-ROM drive.
3. Press R to start the Recovery Console when the "Welcome to Setup" screen appears.
4. Select the installation that you want to access from the Recovery Console.
5. Enter the administrator password and press Enter.
6. Run the command "DISABLE pe386".
7. Type exit
8. Press Enter. The computer will now restart automatically.

2. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain virus definitions:
  • If you use Norton AntiVirus 2006, Symantec AntiVirus Corporate Edition 10.0, or newer products, LiveUpdate definitions are updated daily. These products include newer technology.
  • If you use Norton AntiVirus 2005, Symantec AntiVirus Corporate Edition 9.0, or earlier products, LiveUpdate definitions are updated weekly. The exception is major outbreaks, when definitions are updated more often.
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to Virus Definitions (Intelligent Updater).
  
  The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions. For detailed instructions read the document: How to update virus definition files using the Intelligent Updater.

3. To run a full system scan

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document: How to configure Norton AntiVirus to scan all files.
   • For Symantec AntiVirus Enterprise products: Read the document: How to verify that a Symantec Corporate antivirus product is set to scan all files.
2. Run a full system scan.
3. If any files are detected, follow the instructions displayed by your antivirus program.

Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot delete a detected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe mode. For instructions, read the document, How to start the computer in Safe Mode. Once you have restarted in Safe mode, run the scan again.

After the files are deleted, restart the computer in Normal mode and proceed with the next section.

Warning messages may be displayed when the computer is restarted, since the threat may not be fully removed at this point. You can ignore these messages and click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

Title: [FILE PATH]
Message body: Windows cannot find [FILE NAME]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.


4. To delete the value from the registry
Important: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified subkeys only. For instructions refer to the document: How to make a backup of the Windows registry.

1. Click Start > Run.
2. Type regedit
3. Click OK.
   
   Note: If the registry editor fails to open the threat may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.
   
   
4. Navigate to and delete the subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicespe386
   
   
5. Exit the Registry Editor.