W32.Mydoom.B@mm

SUMMARY

W32.Mydoom.B@mm is a mass-mailing worm that arrives as an attachment with the file extension .bat, .cmd, .exe, .pif, .scr, or .zip.

When a computer is infected, the worm will set up a backdoor into the system, which can potentially allow an attacker to connect to the computer and use it as a proxy to gain access to its network resources.

In addition, the backdoor can download and execute arbitrary files.

The worm will perform a Denial of Service (DoS) against www.microsoft.com starting February 3, 2004 and www.sco.com starting February 1, 2004. It also has a trigger date to stop spreading on March 1, 2004. These events will only occur if the worm is run between or after those dates. While the worm will stop spreading on March 1, 2004, the backdoor component will continue to function after this date.

Note: Symantec Consumer products that support Worm Blocking functionality automatically detect this threat as it attempts to spread.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) January 28, 2004
• Virus Definitions (Intelligent Updater) January 28, 2004

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
• Large Scale E-mailing: Sends to email addresses found in a specified set of files.
• Degrades Performance: May perform a Denial of Service against www.microsoft.com and www.sco.com.
• Compromises Security Settings: Allows unauthorized remote access.

Distribution

• Distribution Level: High
• Subject of Email: Varies
• Name of Attachment: Varies with an extension of .pif, .scr, .exe, .cmd, .bat, or .zip.
• Size of Attachment: 29,184 bytes (varies if it is in .zip format)
• Ports: TCP 80, 1080, 3128, 8080, 10080

TECHNICAL DETAILS

When W32.Mydoom.B@mm is executed, it does the following:

1. Creates the following files:
   
   • %System%Ctfmon.dll: Ctfmon.dll acts as a proxy server. The backdoor also has the ability to download and execute arbitrary files. It makes use of TCP ports 80, 1080, 3128, 8080, and 10080.
   • %Temp%Message: This file contains random letters and is displayed using Notepad.
   • %System%Explorer.exe.
     
     

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     Notes:
   • Explorer.exe is a legitimate file in the Windows 95/98/Me operating systems, but is in the %Windir% folder, not the %System% folder. (By default, this is C:Windows or C:Winnt.) Do not delete the legitimate file that is in the %Windir% folder.
   • %System% is a variable: The worm locates the System folder and copies itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
   • %Temp% is a variable: The worm locates the temporary folder and copies itself to that location. By default, this is C:WindowsTEMP (Windows 95/98/Me), or C:WINNTTemp (Windows NT/2000), or C:Document and Settings<UserName>Local SettingsTemp (Windows XP).

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2. Terminates the taskmon.exe process if it is running.
   
   
3. Adds the value:
   
   "(Default)" = "%System%ctfmon.dll"
   
   to the registry key:
   
   HKEY_CLASSES_ROOTCLSID{E6FB5E20-DE35-11CF-9C87-00AA005127ED}InProcServer32
   
   so that Explorer.exe loads Ctfmon.dll.
   
   
4. Adds the value:
   
   "Explorer" = "%System%Explorer.exe"
   
   to the registry keys:
   
   HKEY_CURRENT_USERSoftwareMicrosftWindowsCurrentVersionRun
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   so that Explorer.exe is run when you start Windows.
   
   
5. Overwrites the local host file to prevent users from accessing the following sites. This action occurs at each instance the worm runs. If the local system date falls within the date range of the www.microsoft.com DoS, the reference to www.microsoft.com is not written to the hosts file.
   
   • ad.doubleclick.net
   • ad.fastclick.net
   • ads.fastclick.net
   • ar.atwola.com
   • atdmt.com
   • avp.ch
   • avp.com
   • avp.ru
   • awaps.net
   • banner.fastclick.net
   • banners.fastclick.net
   • ca.com
   • click.atdmt.com
   • clicks.atdmt.com
   • dispatch.mcafee.com
   • download.mcafee.com
   • download.microsoft.com
   • downloads.microsoft.com
   • engine.awaps.net
   • fastclick.net
   • f-secure.com
   • ftp.f-secure.com
   • ftp.sophos.com
   • go.microsoft.com
   • liveupdate.symantec.com
   • mast.mcafee.com
   • mcafee.com
   • media.fastclick.net
   • msdn.microsoft.com
   • my-etrust.com
   • nai.com
   • networkassociates.com
   • office.microsoft.com
   • phx.corporate-ir.net
   • secure.nai.com
   • securityresponse.symantec.com
   • service1.symantec.com
   • sophos.com
   • spd.atdmt.com
   • support.microsoft.com
   • symantec.com
   • update.symantec.com
   • updates.symantec.com
   • us.mcafee.com
   • vil.nai.com
   • viruslist.ru
   • windowsupdate.microsoft.com
   • www.avp.ch
   • www.avp.com
   • www.avp.ru
   • www.awaps.net
   • www.ca.com
   • www.fastclick.net
   • www.f-secure.com
   • www.kaspersky.ru
   • www.mcafee.com
   • www.microsoft.com
   • www.my-etrust.com
   • www.nai.com
   • www.networkassociates.com
   • www.sophos.com
   • www.symantec.com
   • www.trendmicro.com
   • www.viruslist.ru
   • www3.ca.com
     
     
6. Attempts to perform a DoS attack against www.microsoft.com and www.sco.com.
   • There is a 70% chance that the worm will perform the DoS against www.microsoft.com if the February 3, 2004 trigger date condition has been met.
   • There is an 80% change that the worm will perform the DoS against www.sco.com if the February 1, 2004 trigger date condition has been met.
     
     The DoS against both sites consists of sending GET requests to the target domain using a direct connection to port 80. The date is taken by using the local system time.
     
     
7. Searches for the email addresses in the files that have the following extensions:
   
   • .htm
   • .sht
   • .php
   • .asp
   • .dbx
   • .tbb
   • .adb
   • .pl
   • .wab
   • .txt
     
     
8. Attempts to send email messages using its own SMTP engine. The worm looks up the mail server that the recipient uses before sending the email. It will prepend the following list of strings to the target domain name. If this is unsuccessful, it will use the local mail server instead.
   
   • gate.
   • ns.
   • relay.
   • mail1.
   • mxs.
   • mx1.
   • smtp.
   • mail.
   • mx.
     
     
9. The email will have the following characteristics:
   
   From: The "From" address may be spoofed.
   
   Subject: The subject will be one of the following:
   Returned mail
   Delivery Error
   Status
   Server Report
   Mail Transaction Failed
   Mail Delivery System
   hello
   hi
   
   Message: The message will be one of the following:
   sendmail daemon reported:
   Error #804 occured during SMTP session. Partial message has been received.
   Mail transaction failed. Partial message is available.
   The message contains Unicode characters and has been sent as a binary attachment.
   The message contains MIME-encoded graphics and has been sent as a binary attachment.
   The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment.
   
   Attachment:
   
   The attachment may have either one or two file extensions. If it does have two, the first extension will be one of the following:
   
   .htm
   .txt
   .doc
   
   The second extension, or the only extension if there is only one, will be one of the following:
   .pif
   .scr
   .exe
   .cmd
   .bat
   .zip (This is an actual .zip file that contains a copy of the worm, sharing the same file name as the .zip. For example, readme.zip can contain readme.exe.)
   
   If the worm has an extension of .exe or .scr, the file will be displayed with the following icon:
   
   
   
   
   
   For all the other file extensions, it will use the icon for that file type.
   
   
10. Copies itself to the Kazaa download folder as one of the following files:
    • icq2004-final
    • Xsharez_scanner
    • BlackIce_Firewall_Enterpriseactivation_crack
    • ZapSetup_40_148
    • MS04-01_hotfix
    • Winamp5
    • AttackXP-1.26
    • NessusScan_pro
      
      with a file extension of one of the following:
      
    • .pif
    • .scr
    • .bat
    • .exe
      
      
11. The worm also contains functionality which allows it to install itself on systems which may have been infected by W32.Novarg.A@mm. This is accomplished as follows:
    • The worm creates two to six threads working in parallel.
    • Each thread scans a randomly picked class-C sized networks, from a.b.c.1 to a.b.c.254, except that it skips networks where a=16, 224, 127 or 128.
    • Between each scanned network, a thread waits 128 ms.
    • Each IP in the scanned class-C is contacted on port 3127, if the connection succeeds, the worm sends an update command along with a copy of itself to be executed on the remote machine.

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

Removal using the Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of variants of W32.Novarg/Mydoom. This is the preferred method in most cases.

Manual 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 the entries that were added to the Hosts file.
3. Update the virus definitions.
4. Restart the computer in Safe mode or VGA mode.
5. Run a full system scan and delete all the files detected as W32.Mydoom.B@mm.
6. Delete the values that were added to the registry.
7. Reregister the webcheck.dll file. (This action removes the registry modifications responsible for loading Shimgapi.dll.)
   

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"

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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.

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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. Removing the entries that were added to the Hosts file
If the worm was successful in making changes to the Host file, it may prevent you from running LiveUpdate or accessing certain Web sites.

The Hosts file is not found on all the computers, and if it does exist, the location can vary. For example, if the file exists in Windows 98, it will usually be in C:Windows; and in Windows 2000, it is in the C:WINNTSYSTEM32DRIVERSETC folder. Also, there may be multiple copies of this file in different locations.

The most efficient way to locate the file is to search for it.

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 one 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, within the file, delete all the entries in the Hosts file where the line begins with 0.0.0.0.
     
     For example:
     
     0.0.0.0     www.microsoft.com
     
     There may be many lines like this. Delete all of them.
     
     
  9. Close Notepad and save your changes when prompted.
     
     
• Windows XP
  1. Click Start, and then click 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 one 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, within the file, delete all the entries in the Hosts file where the line begins with 0.0.0.0.
      
      For example:
      
      0.0.0.0     www.microsoft.com
      
      There may be many lines like this. Delete all of them.
      
      
  14. Close Notepad and save your changes when prompted.
      

3. 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.

4. Restarting 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.

5. 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.Mydoom.B@mm, click Delete.

6. Reversing the changes that were made to the registry

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WARNING: 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.

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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 each of these keys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete the value:
   
   "Explorer"="%System%explorer.exe"
   
   

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   Note: %System% is a variable that refers to the location of the System folder. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).

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5. Exit the Registry Editor.

7. Reregistering the Webcheck.dll file
This action removes the registry modifications responsible for loading Shimgapi.dll.

1. Click Start, and then click Run. (The Run dialog box appears.)
2. Type, or copy and paste, the following text:
   
   regsvr32 webcheck.dll
   
   
3. Click OK. When you see the message, "DllRegisterServer in webcheck.dll
   succeeded," click OK.