W32.Theals.A@mm

SUMMARY

W32.Theals.A@mm is a mass-mailing worm that sends itself as password protected .zip file. The worm is also able to spread across the local network by exploiting vulnerabilities and can hide itself using rootkit functionalities. The worm steals confidential information and WebMoney files.

Protection

• Virus Definitions (LiveUpdate™ Weekly) September 7, 2005
• Virus Definitions (Intelligent Updater) September 2, 2005

Threat Assessment

Wild

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

Damage

• Damage Level: Medium
• Payload: Tries to perform a distributed denial of service.
• Large Scale E-mailing: Mass-mailing worm that sends itself as password protected .zip file.
• Modifies Files: Injects its malicious code in specific processes.
• Releases Confidential Info: Collects the operating system version and country and sends it to a URL.
• Degrades Performance: Mass-mailing may degrade performance.
• Compromises Security Settings: Overwrites the hosts file to block access to security related Web sites.

Distribution

• Distribution Level: High
• Name of Attachment: Varies
• Ports: TCP port 80

TECHNICAL DETAILS

When W32.Theals.A@mm is executed, it performs the following actions:

1. Arrives in an email as a unique file that drops all the other components. The dropper could be an executable file or an .hta file.
   
   
2. Creates and executes the following files:
   
   • C:stealth.exe
   • C:stealth.dcom.exe
   • C:stealth.ddos.exe
   • C:stealth.injector.exe
   • C:stealth.stat.exe
   • C:stealth.wm.exe
   • C:stealth.worm.exe
   • C:stealth.shared.dll
   • C:stealth.bszip.dll
     
     Note: The file C:stealth.bszip.dll is a clean compression library used by the worm. All of the files require the stealth.shared.dll library to work.
     
     
3. Adds the values:
   
   "stealth.exe" = "C:stealth.exe"
   "stealth.dcom.exe" = "C:stealth.dcom.exe"
   "stealth.ddos.exe" = "C:stealth.ddos.exe"
   "stealth.injector.exe" = "C:stealth.injector.exe"
   "stealth.stat.exe" = "C:stealth.stat.exe"
   "stealth.wm.exe" = "C:stealth.wm.exe"
   "stealth.worm.exe" = "C:stealth.worm.exe"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that it runs every time Windows starts.
   
   
4. Hides its presence by hooking the following Windows APIs:
   
   
   • RegEnumValueA
   • RegEnumValueW
   • FindNextFileA
   • FindNextFileW
   • Process32Next
     
     
5. Works as a rootkit and hides all files, processes, and registry subkeys that begin with the string "stealth".
   
   
6. Generates a random password of 12 digits and writes it as bitmap image in the following file:
   
   C:stealth.pass.bmp
   
   
7. Copies the installer using a random file name with a random extension that could be one of the following:
   
   
   • .exe
   • .scr
   • .bat
     
     
8. Puts this file into a ZIP archive, which is protected with the random password in the stealth.pass.bmp file:
   
   C:stealth.worm.zip
   
   
9. Searches for the following processes in memory, executing the mass-mailing routine each time they are found:
   
   
   • msimn.exe
   • outlook.exe
   • thebat.exe
     
     
10. Injects its malicious code inside these processes, altering the functioning of "ws2_32.send()" API.
    
    
11. Sends itself as an attachment to an email with the following characteristics:
    
    Message Body:
    
    ZIP PASSWORD:
    
    Note: The message includes a bitmap image.
    
    Attachment:
    One of the following names:
    
    
    • Document.zip
    • Foto.zip
    • Secret.zip
    • PORNO.zip
    • Tetris.zip
      
      
12. Intercepts the following strings and collects them in the file C:stealth.injector.rpt during the mail spreading process:
    
    
    • USER
    • PASS
      
      
13. Gathers the current IP address and generates IP addresses that would reside on a local network A.B.C.X, where X is a number between 1 and 254.
    
    
14. Copies itself to vulnerable computers on the local network by exploiting the Microsoft Windows DCOM RPC Interface Buffer Overrun Vulnerability (described in Microsoft Security Bulletin MS03-026).
    
    
15. Tries to perform a distributed denial of service against the following Web sites, sending randomly generated packets over TCP port 80:
    
    
    • kaspersky.com
    • kaspersky.ru
      
      
16. Overwrites the hosts file with the following entries:
    
    127.0.0.1 ad.doubleclick.net
    127.0.0.1 ad.fastclick.net
    127.0.0.1 ads.fastclick.net
    127.0.0.1 ar.atwola.com
    127.0.0.1 atdmt.com
    127.0.0.1 avp.ch
    127.0.0.1 avp.com
    127.0.0.1 avp.com
    127.0.0.1 avp.ru
    127.0.0.1 awaps.net
    127.0.0.1 banner.fastclick.net
    127.0.0.1 banners.fastclick.net
    127.0.0.1 ca.com
    127.0.0.1 ca.com
    127.0.0.1 click.atdmt.com
    127.0.0.1 clicks.atdmt.com
    127.0.0.1 customer.symantec.com
    127.0.0.1 dispatch.mcafee.com
    127.0.0.1 dispatch.mcafee.com
    127.0.0.1 download.mcafee.com
    127.0.0.1 download.mcafee.com
    127.0.0.1 download.mcafee.com
    127.0.0.1 download.microsoft.com
    127.0.0.1 downloads.microsoft.com
    127.0.0.1 downloads1.kaspersky-labs.com
    127.0.0.1 downloads1.kaspersky-labs.com
    127.0.0.1 downloads1.kaspersky-labs.com/updates
    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-us2.kaspersky-labs.com
    127.0.0.1 downloads-us3.kaspersky-labs.com
    127.0.0.1 engine.awaps.net
    127.0.0.1 fastclick.net
    127.0.0.1 f-secure.com
    127.0.0.1 f-secure.com
    127.0.0.1 ftp.avp.ch
    127.0.0.1 ftp.downloads2.kaspersky-labs.com
    127.0.0.1 ftp.f-secure.com
    127.0.0.1 ftp.kasperskylab.ru
    127.0.0.1 ftp.sophos.com
    127.0.0.1 go.microsoft.com
    127.0.0.1 ids.kaspersky-labs.com
    127.0.0.1 kaspersky.com
    127.0.0.1 kaspersky-labs.com
    127.0.0.1 liveupdate.symantec.com
    127.0.0.1 liveupdate.symantec.com
    127.0.0.1 liveupdate.symantec.com
    127.0.0.1 liveupdate.symantecliveupdate.com
    127.0.0.1 liveupdate.symantecliveupdate.com
    127.0.0.1 localhost
    127.0.0.1 mast.mcafee.com
    127.0.0.1 mast.mcafee.com
    127.0.0.1 mcafee.com
    127.0.0.1 mcafee.com
    127.0.0.1 media.fastclick.net
    127.0.0.1 msdn.microsoft.com
    127.0.0.1 my-etrust.com
    127.0.0.1 my-etrust.com
    127.0.0.1 nai.com
    127.0.0.1 nai.com
    127.0.0.1 networkassociates.com
    127.0.0.1 networkassociates.com
    127.0.0.1 office.microsoft.com
    127.0.0.1 phx.corporate-ir.net
    127.0.0.1 rads.mcafee.com
    127.0.0.1 secure.nai.com
    127.0.0.1 secure.nai.com
    127.0.0.1 securityresponse.symantec.com
    127.0.0.1 securityresponse.symantec.com
    127.0.0.1 service1.symantec.com
    127.0.0.1 sophos.com
    127.0.0.1 sophos.com
    127.0.0.1 spd.atdmt.com
    127.0.0.1 support.microsoft.com
    127.0.0.1 symantec.com
    127.0.0.1 symantec.com
    127.0.0.1 trendmicro.com
    127.0.0.1 update.symantec.com
    127.0.0.1 update.symantec.com
    127.0.0.1 update.symantec.com
    127.0.0.1 updates.symantec.com
    127.0.0.1 updates.symantec.com
    127.0.0.1 updates1.kaspersky-labs.com
    127.0.0.1 updates1.kaspersky-labs.com
    127.0.0.1 updates2.kaspersky-labs.com
    127.0.0.1 updates3.kaspersky-labs.com
    127.0.0.1 updates3.kaspersky-labs.com/updates
    127.0.0.1 updates4.kaspersky-labs.com
    127.0.0.1 updates5.kaspersky-labs.com
    127.0.0.1 us.mcafee.com
    127.0.0.1 us.mcafee.com
    127.0.0.1 vil.nai.com
    127.0.0.1 viruslist.com
    127.0.0.1 viruslist.ru
    127.0.0.1 windowsupdate.microsoft.com
    127.0.0.1 www.avp.ch
    127.0.0.1 www.avp.com
    127.0.0.1 www.avp.com
    127.0.0.1 www.avp.ru
    127.0.0.1 www.awaps.net
    127.0.0.1 www.ca.com
    127.0.0.1 www.ca.com
    127.0.0.1 www.fastclick.net
    127.0.0.1 www.f-secure.com
    127.0.0.1 www.f-secure.com
    127.0.0.1 www.grisoft.com
    127.0.0.1 www.kaspersky.com
    127.0.0.1 www.kaspersky.ru
    127.0.0.1 www.kaspersky.ru
    127.0.0.1 www.kaspersky-labs.com
    127.0.0.1 www.mcafee.com
    127.0.0.1 www.mcafee.com
    127.0.0.1 www.my-etrust.com
    127.0.0.1 www.my-etrust.com
    127.0.0.1 www.nai.com
    127.0.0.1 www.nai.com
    127.0.0.1 www.networkassociates.com
    127.0.0.1 www.networkassociates.com
    127.0.0.1 www.sophos.com
    127.0.0.1 www.sophos.com
    127.0.0.1 www.symantec.com
    127.0.0.1 www.symantec.com
    127.0.0.1 www.trendmicro.com
    127.0.0.1 www.trendmicro.com
    127.0.0.1 www.viruslist.com
    127.0.0.1 www.viruslist.ru
    127.0.0.1 www3.ca.com
    
    
17. Collects the operating system version and country of the compromised computer and sends it to the following URL:
    
    [http://]lacrimosa1.hut1.ru/[REMOVED]/stat.php?os=[OS_TYPE]&country=[OS_COUNTRY]
    
    
18. Periodically scans the process list looking for the webmoney.exe program. If found, the worm collects WebMoney files when they are accessed. The files, reports, and accounts are saved as the following files:
    
    
    • C:stealth.wm.rpt
    • C:stealth.wm.kvm
    • C:stealth.wm.pwm
    • C:stealth.wm
      
      
19. Sends files to a predetermined email address on the mail.ru domain, using smtp.mail.ru as the outgoing email server.

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. Remove all the entries that the risk added to the hosts file.
3. Update the virus definitions.
4. Run a full system scan and delete all the files detected.
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 remove all the entries that the risk added to the hosts file

1. Navigate to the following location:
   
   
   • Windows 95/98/Me:
     %Windir%
   • Windows NT/2000/XP:
     %Windir%System32driversetc
     
     Notes:
   • The location of the hosts file may vary and some computers may not have this file. There may also be multiple copies of this file in different locations. If the file is not located in these folders, search your disk drives for the hosts file, and then complete the following steps for each instance found.
   • %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows (Windows 95/98/Me/XP) or C:Winnt (Windows NT/2000).
     
     
2. Double-click the hosts file.
3. If necessary, deselect the "Always use this program to open this program" check box.
4. Scroll through the list of programs and double-click Notepad.
5. When the file opens, delete all the entries added by the risk. (See the Technical Details section for a complete list of entries.)
6. Close Notepad and save your changes when prompted.

3. 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 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 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.

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.
   • 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, click Delete.

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.


5. 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 the subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
5. In the right pane, delete the values:
   
   "stealth.exe" = "C:stealth.exe"
   "stealth.dcom.exe" = "C:stealth.dcom.exe"
   "stealth.ddos.exe" = "C:stealth.ddos.exe"
   "stealth.injector.exe" = "C:stealth.injector.exe"
   "stealth.stat.exe" = "C:stealth.stat.exe"
   "stealth.wm.exe" = "C:stealth.wm.exe"
   "stealth.worm.exe" = "C:stealth.worm.exe"
   
   
6. Exit the Registry Editor.