W32.Randex.D

SUMMARY

W32.Randex.D is a network-aware worm that will copy itself to the following paths on computers with weak administrator passwords:

• Admin$system32msmsgri32.exe
• c$winntsystem32msmsgri32.exe

The worm will also drop a Backdoor Trojan detected as Backdoor.Roxy, which will listen on the following TCP ports:

• 3330
• 3331
• 3332
• 3361

NOTE:

• The virus definitions dated prior to July 31, 2003 detect the dropped file as Backdoor.Trojan.
• The detection for W32.Randex.D was updated in virus definitions dated August 6, 2003 to account for the discovery of a minor variant. This file exhibited the same characteristics as previous samples.

Protection

• Virus Definitions (LiveUpdate™ Weekly) June 28, 2003
• Virus Definitions (Intelligent Updater) June 28, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 50 - 999
• Number of Sites: More than 10
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Medium
• Compromises Security Settings: Allows unauthorized remote access.

Distribution

• Distribution Level: Medium
• Ports: TCP 3330, 3331, 3332, 3361
• Shared Drives: Attempts to copy itself to administrative shares with weak passwords.

TECHNICAL DETAILS

When W32.Randex.D is executed, it does the following:

1. Attempts to authenticate to randomly generated IP addresses. The user account list for that remote machine is enumerated, using the NetUserEnum() API. The worm will try connecting as everyone in the list of users who exist on the remote machine until it successfully connects or runs out of accounts.
   
   The worm attempts this action by using one of the following passwords:
   • <blank>
   • admin
   • root
   • 1
   • 111
   • 123
   • 1234
   • 123456
   • 654321
   • !@#$
   • asdf
   • asdfgh
   • !@#$%
   • !@#$%^
   • !@#$%^&
   • !@#$%^&*
   • server
     
     This action result in accounts being locked out due to unsuccessful log on attempts.
     
     
2. Copies itself to computers, with weak administrator passwords, as the following:
   • \<authenticated IP>Admin$system32msmsgri32.exe
   • \<authenticated IP>c$winntsystem32msmsgri32.exe
     
     
3. Schedules a network job to run the worm.
   
   
4. Adds the value:
   
   "mssyslanhelper"="msmsgri32.exe"
   
   or
   
   "mslanhelper"="msmsgri32.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the worm runs when you start Windows.
   
   
5. Creates and runs Backdoor.Roxy as Payload.dat. The Backdoor Trojan adds the value:
   
   "System Initialization"="payload.dat"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the Backdoor.Trojan runs when you start Windows.
   
   
6. The Backdoor.Trojan sends a notification to a hard-coded IP address, indicating that it is running.
   
   
7. The Backdoor.Trojan listens on the following TCP ports for remote instructions:
   • port 3330
   • port 3331
   • port 3332

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. Update the virus definitions.
3. Restart the computer in Safe mode or VGA mode.
4. Run a full system scan and delete all the files detected as W32.Randex.D.
5. Delete the value that was added to the registry.
   

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

1. Disabling 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"

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. Updating 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 on U.S. business days (Monday through Friday). 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. Restarting 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 on restarting in Safe mode, refer to the document, "How to start the computer in Safe Mode."
• For Windows NT 4 users, restart the computer in VGA mode.

4. Scanning for and deleting the infected files

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 as infected with W32.Randex.D, click Delete.

5. Deleting the value from the registry

CAUTION: 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, and then click Run. (The Run dialog box appears.)
2. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete the values:
   
   "mssyslanhelper"="<worm filename>"
   "mslanhelper"="<worm filename>"
   "System Initialization"="<backdoor filename>"
   
   
5. Exit the Registry Editor.