Backdoor.Nemog.B

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Discovered: September 09, 2004
Updated: February 13, 2007 12:27:16 PM
Type: Trojan Horse
Systems Affected: Windows


Backdoor.Nemog.B is a backdoor Trojan horse program that allows an infected computer to be used as an email relay and http proxy. The Trojan also blocks access to several security related Web sites.

Antivirus Protection Dates

  • Initial Rapid Release version September 09, 2004
  • Latest Rapid Release version August 20, 2008 revision 017
  • Initial Daily Certified version September 09, 2004
  • Latest Daily Certified version August 20, 2008 revision 016
  • Initial Weekly Certified release date September 15, 2004

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Kaoru Hayashi

Discovered: September 09, 2004
Updated: February 13, 2007 12:27:16 PM
Type: Trojan Horse
Systems Affected: Windows


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

  1. Creates the following files:

    %System%\dx32cxlp.exe
    %System%\dx32cxel.sys

  2. Creates the following registry keys:

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\dx32cxel
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_DX32CXEL

    to create the service dx32cxel, so that the Trojan executes every time Windows starts.

  3. Hides its service and files by hooking several APIs and by returning null results for any API calls.

  4. Contacts the following servers using TCP port 4242, 4646, 4661, 3306, or 8080:
    • 62.241.53.2
    • 211.233.41.235
    • 81.23.250.167
    • 193.19.227.24
    • 66.98.192.99
    • 207.44.222.47
    • 213.158.119.104
    • 207.44.206.27
    • 62.241.53.4
    • 216.127.94.107
    • 67.15.18.45
    • 62.241.53.15
    • 64.246.54.12
    • 62.241.53.16
    • 211.214.161.107
    • 67.15.18.57
    • 66.98.144.100
    • 69.50.187.210
    • 66.111.43.80
    • 212.199.125.36
    • 66.90.68.2:6565
    • 62.241.53.17
    • 69.50.228.50
    • 81.23.250.169
    • 69.57.132.8
    • 64.246.18.98
    • 218.78.211.62
    • 207.44.142.33
    • 64.246.16.11
    • 205.209.176.220
    • 80.64.179.46
    • 65.75.161.70

  5. Relay's emails from remote users through a randomly chosen TCP port, and runs as an http proxy server on another randomly chosen TCP port.

  6. Receives commands from a remote attacker through a backdoor to perform the following actions:
    • Uninstall itself
    • Update itself
    • Download a file

  7. Prevents access to several security related Web sites by overwriting the %System%\DRIVERS\ETC\HOSTS file with the following text:
    127.0.0.1 www.avp.com
    127.0.0.1 www.viruslist.com
    127.0.0.1 viruslist.com
    127.0.0.1 www.symantec.com
    127.0.0.1 networkassociates.com
    127.0.0.1 secure.nai.com
    127.0.0.1 downloads1.kaspersky-labs.com
    127.0.0.1 downloads2.kaspersky-labs.com
    127.0.0.1 downloads3.kaspersky-labs.com
    127.0.0.1 downloads4.kaspersky-labs.com
    127.0.0.1 downloads-us1.kaspersky-labs.com
    127.0.0.1 downloads-eu1.kaspersky-labs.com
    127.0.0.1 kaspersky-labs.com
    127.0.0.1 www.networkassociates.com
    127.0.0.1 us.mcafee.com
    127.0.0.1 f-secure.com
    127.0.0.1 avp.com
    127.0.0.1 www.sophos.com
    127.0.0.1 sophos.com
    127.0.0.1 www.ca.com
    127.0.0.1 ca.com
    127.0.0.1 securityresponse.symantec.com
    127.0.0.1 symantec.com
    127.0.0.1 mast.mcafee.com
    127.0.0.1 my-etrust.com
    127.0.0.1 www.kaspersky.com
    127.0.0.1 www.f-secure.com
    127.0.0.1 dispatch.mcafee.com
    127.0.0.1 update.symantec.com
    127.0.0.1 nai.com
    127.0.0.1 www.nai.com
    127.0.0.1 liveupdate.symantec.com
    127.0.0.1 customer.symantec.com
    127.0.0.1 rads.mcafee.com
    127.0.0.1 trendmicro.com
    127.0.0.1 liveupdate.symantecliveupdate.com
    127.0.0.1 www.mcafee.com
    127.0.0.1 mcafee.com
    127.0.0.1 viruslist.com
    127.0.0.1 www.my-etrust.com
    127.0.0.1 download.mcafee.com
    127.0.0.1 updates.symantec.com
    127.0.0.1 kaspersky.com
    127.0.0.1 www.trendmicro.com 


Recommendations

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: Kaoru Hayashi

Discovered: September 09, 2004
Updated: February 13, 2007 12:27:16 PM
Type: Trojan Horse
Systems Affected: Windows


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. Update the virus definitions.
  3. To restart the computer in Safe mode or VGA mode.
  4. Run a full system scan and delete all the files detected as Backdoor.Nemog.B.
  5. Reverse the changes made to the registry.
  6. To delete the added lines from the Windows Hosts file.
For 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:

Note:
When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable 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 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: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • 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 the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. To restart the computer in Safe mode or VGA mode

Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.
  • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
  • For Windows NT 4 users, restart the computer in VGA mode.
4. To scan for and delete the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with Backdoor.Nemog.B, click Delete.

5. To reverse the changes made to 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 keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

  1. Click Start > Run.
  2. Type regedit

    Then click OK.

  3. Navigate to and delete the keys:

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\dx32cxel
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_DX32CXEL

  4. Exit the Registry Editor.


6. To delete the added lines from the Windows Hosts file


Note: The location of the Hosts file may vary and some computers may not have this file. For example, if the file exists in Windows 98, it will usually be in C:\Windows; and it is located in the C:\WINNT\system32\drivers\etc folder in Windows 2000. There may also be multiple copies of this file in different locations.


Follow the instructions for your operating system:
  • Windows 95/98/Me/NT/2000
    1. Click Start, point to Find or Search, and then click Files or Folders.
    2. Make sure that "Look in" is set to (C:) and that "Include subfolders" is checked.
    3. In the "Named" or "Search for..." box, type:

      hosts

    4. Click Find Now or Search Now.
    5. For each Hosts file that you find, right-click the file, and then click Open With.
    6. Deselect the "Always use this program to open this program" check box.
    7. Scroll through the list of programs and double-click Notepad.
    8. When the file opens, delete the following entries in the Hosts file:

      127.0.0.1 www.avp.com
      127.0.0.1 www.viruslist.com
      127.0.0.1 viruslist.com
      127.0.0.1 www.symantec.com
      127.0.0.1 networkassociates.com
      127.0.0.1 secure.nai.com
      127.0.0.1 downloads1.kaspersky-labs.com
      127.0.0.1 downloads2.kaspersky-labs.com
      127.0.0.1 downloads3.kaspersky-labs.com
      127.0.0.1 downloads4.kaspersky-labs.com
      127.0.0.1 downloads-us1.kaspersky-labs.com
      127.0.0.1 downloads-eu1.kaspersky-labs.com
      127.0.0.1 kaspersky-labs.com
      127.0.0.1 www.networkassociates.com
      127.0.0.1 us.mcafee.com
      127.0.0.1 f-secure.com
      127.0.0.1 avp.com
      127.0.0.1 www.sophos.com
      127.0.0.1 sophos.com
      127.0.0.1 www.ca.com
      127.0.0.1 ca.com
      127.0.0.1 securityresponse.symantec.com
      127.0.0.1 symantec.com
      127.0.0.1 mast.mcafee.com
      127.0.0.1 my-etrust.com
      127.0.0.1 www.kaspersky.com
      127.0.0.1 www.f-secure.com
      127.0.0.1 dispatch.mcafee.com
      127.0.0.1 update.symantec.com
      127.0.0.1 nai.com
      127.0.0.1 www.nai.com
      127.0.0.1 liveupdate.symantec.com
      127.0.0.1 customer.symantec.com
      127.0.0.1 rads.mcafee.com
      127.0.0.1 trendmicro.com
      127.0.0.1 liveupdate.symantecliveupdate.com
      127.0.0.1 www.mcafee.com
      127.0.0.1 mcafee.com
      127.0.0.1 viruslist.com
      127.0.0.1 www.my-etrust.com
      127.0.0.1 download.mcafee.com
      127.0.0.1 updates.symantec.com
      127.0.0.1 kaspersky.com
      127.0.0.1 www.trendmicro.com

    9. Close Notepad and save your changes when prompted.

  • Windows XP
    1. Click Start > Search.
    2. Click All files and folders.
    3. In the "All or part of the file name" box, type:

      hosts

    4. Verify that "Look in" is set to "Local Hard Drives" or to (C:).
    5. Click More advanced options.
    6. Check Search system folders.
    7. Check Search subfolders.
    8. Click Search.
    9. Click Find Now or Search Now.
    10. For each Hosts file that you find, right-click the file, and then click Open With.
    11. Deselect the Always use this program to open this program check box.
    12. Scroll through the list of programs and double-click Notepad.
    13. When the file opens, delete the following entries in the Hosts file:

      127.0.0.1 www.avp.com
      127.0.0.1 www.viruslist.com
      127.0.0.1 viruslist.com
      127.0.0.1 www.symantec.com
      127.0.0.1 networkassociates.com
      127.0.0.1 secure.nai.com
      127.0.0.1 downloads1.kaspersky-labs.com
      127.0.0.1 downloads2.kaspersky-labs.com
      127.0.0.1 downloads3.kaspersky-labs.com
      127.0.0.1 downloads4.kaspersky-labs.com
      127.0.0.1 downloads-us1.kaspersky-labs.com
      127.0.0.1 downloads-eu1.kaspersky-labs.com
      127.0.0.1 kaspersky-labs.com
      127.0.0.1 www.networkassociates.com
      127.0.0.1 us.mcafee.com
      127.0.0.1 f-secure.com
      127.0.0.1 avp.com
      127.0.0.1 www.sophos.com
      127.0.0.1 sophos.com
      127.0.0.1 www.ca.com
      127.0.0.1 ca.com
      127.0.0.1 securityresponse.symantec.com
      127.0.0.1 symantec.com
      127.0.0.1 mast.mcafee.com
      127.0.0.1 my-etrust.com
      127.0.0.1 www.kaspersky.com
      127.0.0.1 www.f-secure.com
      127.0.0.1 dispatch.mcafee.com
      127.0.0.1 update.symantec.com
      127.0.0.1 nai.com
      127.0.0.1 www.nai.com
      127.0.0.1 liveupdate.symantec.com
      127.0.0.1 customer.symantec.com
      127.0.0.1 rads.mcafee.com
      127.0.0.1 trendmicro.com
      127.0.0.1 liveupdate.symantecliveupdate.com
      127.0.0.1 www.mcafee.com
      127.0.0.1 mcafee.com
      127.0.0.1 viruslist.com
      127.0.0.1 www.my-etrust.com
      127.0.0.1 download.mcafee.com
      127.0.0.1 updates.symantec.com
      127.0.0.1 kaspersky.com
      127.0.0.1 www.trendmicro.com

    14. Close Notepad and save your changes when prompted.


Writeup By: Kaoru Hayashi