W32.Lorac

SUMMARY

W32.Lorac is a network aware worm that allows remote control of an infected system, via HTTP.

This worm has been distributed as an email attachment named Message.zip. An HTML file, which contains the worm, exists inside the zip file. The worm takes advantage of a vulnerability described in MS03-14, which allows for the execution of a MIME-encoded program inside an HTML file.

NOTE: Definitions dated prior to Octomer 9, 2003 may detect this as Backdoor.Lorac.

Protection

• Virus Definitions (LiveUpdate™ Weekly) August 27, 2003
• Virus Definitions (Intelligent Updater) August 22, 2003

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
• Large Scale E-mailing: N/A
• Deletes Files: N/A
• Modifies Files: N/A
• Releases Confidential Info: N/A
• Degrades Performance: N/A
• Causes System Instability: N/A
• Compromises Security Settings: Allows remote access through HTTP.

Distribution

• Distribution Level: Low
• Name of Attachment: message.zip
• Size of Attachment: 36108
• Ports: N/A
• Shared Drives: Copies itself to across network shares
• Target of Infection: N/A
• Time Stamp of Attachment: N/A

TECHNICAL DETAILS

When W32.Lorac is executed, it does the following:

1. Generates a filename of the form abcdef.exe. The actual filename is a function of the volume serial number, so the name will be different for every computer.
   
   
2. Copies itself to the System folder using the generated filename.
   
   
3. Adds the value:
   
   "<four random characters>"= "%Sysdir%abcdef.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   so that the worm runs when you start Windows.
   
   
4. Queries the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion
   ExplorerShell FoldersCommon Startup
   
   and copies itself to this folder as Explorer.exe.
   
5. Enumerates all network resources to locate remote machines.
   
6. Queries the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion
   ExplorerShell FoldersCommon Startup
   
   on the remote machine to locate the Startup folder.
   
7. Copies itself to this folder as Explorer.exe.
   
8. Uses an internal SMTP client to send email notification to a certain address.
   
   
9. Periodically downloads a file from a certain Web site. This file contains commands that control the execution of the worm. Depending on the commands that the worm receives, the worm may:
   • Retrieve system information
   • Manipulate files (copy, move, create, or delete)
   • Upload and download files
   • Execute arbitrary programs

All communication between the backdoor and the remote system takes place via HTTP transactions. The resulting network activity will resemble normal HTTP traffic.

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.Lorac.
4. 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. 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.Lorac, note the filename, and then click Delete.

NOTE: If your Symantec antivirus product reports that it cannot delete an infected file, shut down the computer, turn off the power, and wait 30 seconds. Restart the computer in Safe mode (Windows 95/98/Me/2000/XP) or VGA mode (Windows NT 4), and then run the scan again.

For instructions on how to restart in Safe mode, read the document, "How to start the computer in Safe Mode."

4. 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 value that refers to the worm file (noted earlier). This value has the form:
   
   "<four random characters>"="%Sysdir%<filename>.exe"
   
   
5. Exit the Registry Editor.