W32.Toxbot

SUMMARY

W32.Toxbot is a worm that opens an IRC back door on the compromised computer and spreads by exploiting vulnerabilities.

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 13, 2005
• Virus Definitions (Intelligent Updater) March 10, 2005

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: Low
• Payload: Opens a back door.
• Releases Confidential Info: Logs keystrokes and steals passwords.
• Degrades Performance: Downloads remote files and may degrade network performance.

Distribution

• Distribution Level: Medium
• Target of Infection: Computers with remotely exploitable vulnerabilities.

TECHNICAL DETAILS

When W32.Toxbot is executed, it performs the following actions:

1. Creates a copy of itself as %System%[RANDOM FILE NAME].exe.
   
   Note:
   • %System% is a variable that refers to the System folder. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
   • [RANDOM FILE NAME] is usually 8 characters long. Possible examples of [RANDOM FILE NAME] include:
     
     
     • TrkWksrv.exe
     • dxdllsvc.exe
     • ciclient.exe
     • dhcpclient.exe
       
       
2. May create a service with the following properties:
   
   Service Name: DHCP Client
   Display Name: Handling the DHCP requests
   
   
3. In creating the above service, the following registry entries are created:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSafeBootMinimalDHCP Client"@" = "Service"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSafeBootNetworkDHCP Client"@" = "Service"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT000Control"*NewlyCreated*" = "0x00000000"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT000Control"ActiveService" = "DHCP Client"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT000"Service" = "DHCP Client"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT000"Legacy" = "0x00000001"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT000ConfigFlags: "0x00000000"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT000"Class" = "LegacyDriver"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT000"ClassGUID" = "{8ECC055D-047F-11D1-A537-0000F8753ED1}"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT000"DeviceDesc" = "Handling the DHCP requests"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT"NextInstance" = "0x00000001"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP ClientEnum"0" = "RootLEGACY_DHCP_CLIENT000"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP ClientEnum"Count" = "0x00000001"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP ClientEnum"NextInstance" = "0x00000001"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP ClientSecurity"Security" = "01 00 14 80 90 00 00 00 9C 00 00 00 14 00 00 00 30 00 00 00 02 00 1C 00 01 00 00 00 02 80 14 00 FF 01 0F 00 01 01 00 00 00 00 00 01 00 00 00 00 02 00 60 00 04 00 00 00 00 00 14 00 FD 01 02 00 01 01 00 00 00 00 00 05 12 00 00 00 00 00 18 00 FF 01 0F 00 01 02 00 00 00 00 00 05 20 00 00 00 20 02 00 00 00 00 14 00 8D 01 02 00 01 01 00 00 00 00 00 05 0B 00 00 00 00 00 18 00 FD 01 02 00 01 02 00 00 00 00 00 05 20 00 00 00 23 02 00 00 01 01 00 00 00 00 00 05 12 00 00 00 01 01 00 00 00 00 00 05 12 00 00 00"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP Client"Type" = "0x00000110"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP Client"Start" = "0x00000002"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP Client"ErrorControl" = "0x00000000"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP Client"ImagePath" = "%System%dhcpclient.exe"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP Client"DisplayName" = "Handling the DHCP requests"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP Client"ObjectName" = "LocalSystem"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP Client"FailureActions" = "05 00 00 00 00 00 00 00 00 00 00 00 01 00 00 00 41 00 63 00 01 00 00 00 01 00 00 00"
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP Client"Description" = "Manages network configuration by registering and updating IP addresses and DNS names."
   
   
4. Adds the value:
   
   "[DEFAULT]" = "Service"
   
   to the registry subkeys:
   
   HKEY_LOCAL_MACHINESystemCurrentControlSetControlSafeBootMinimal[RANDOM FILE NAME]
   HKEY_LOCAL_MACHINESystemCurrentControlSetControlSafeBootNetwork[RANDOM FILE NAME]
   
   so that it is executed every time Windows starts.
   
   
5. Adds the registry subkeys:
   
   HKEY_LOCAL_MACHINESystemCurrentControlSetEnumRootLEGACY_[RANDOM FILE NAME]
   HKEY_LOCAL_MACHINESystemCurrentControlSetServices[RANDOM FILE NAME]
   
   
6. Contacts an IRC server on one of the following domains:
   
   
   • 5555.devtech.us
   • 5555.memzero.info
   • 99DEADBEEF.goingformars.com
   • 99DEADBEEF.martiansong.com
   • 99DEADBEEF.my1x1.com
   • 99DEADBEEF.my-secure.name
     
     
7. The back door allows the remote attacker to perform the following actions:
   
   
   • Log keystrokes
   • End processes
   • Steal cached passwords
   • Steal system information
   • Download remote files
     
     
8. Spreads by exploiting the following vulnerabilities:
   
   
   • The Microsoft Windows DCOM RPC Interface Buffer Overrun Vulnerability (described in Microsoft Security Bulletin MS03-026).
   • The Microsoft Windows ntdll.dll Buffer Overflow Vulnerability (described in Microsoft Security Bulletin MS03-007).
   • The Microsoft SQL Server Web Task Stored Procedure Privilege Escalation Vulnerability (as described in Microsoft Security Bulletin MS02-061).
     
     
9. Attempts to spread to computers running MS Sql Server with weak passwords, by opening a connection using the default username "sa", and the following passwords:
   
   
   • sa
   • root
   • admin
     
     
10. Checks for the presence of the virtual infrastructure software VMware by searching for the registry subkey HKEY_LOCAL_MACHINESoftwareVMware. The worm will not run on computers running this software.

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. Run a full system scan and delete all the files detected as W32.Toxbot.
4. Delete the value that was 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, 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 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.
   • 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.Toxbot, click Delete.
   
   Note: If your Symantec antivirus product reports that it cannot delete an infected file, Windows may be using the file. To fix 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 section 4.
   

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. 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 the subkeys:
   
   HKEY_LOCAL_MACHINESystemCurrentControlSetControlSafeBootMinimal[RANDOM FILE NAME]
   HKEY_LOCAL_MACHINESystemCurrentControlSetControlSafeBootNetwork[RANDOM FILE NAME]
   
   
4. In the right pane, delete the value:
   
   "[DEFAULT]" = "Service"
   
   
5. Navigate to and delete the registry subkeys:
   
   HKEY_LOCAL_MACHINESystemCurrentControlSetEnumRootLEGACY_[RANDOM FILE NAME]
   HKEY_LOCAL_MACHINESystemCurrentControlSetServices[RANDOM FILE NAME]
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSafeBootMinimalDHCP Client
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSafeBootNetworkDHCP Client
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_DHCP_CLIENT
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDHCP Client
   
   
6. Exit the Registry Editor.