Discovered: December 16, 2002
Updated: February 13, 2007 11:41:36 AM
Also Known As: I-WORM.Lentin.h [KAV]
Type: Worm
Systems Affected: Windows



W32.Yaha.H@mm is a variant of W32.Yaha@mm . It sends itself to all email addresses that exist in the Microsoft Windows Address Book, the MSN Messenger List, the Yahoo Pager list, and to specific email addresses that are contained in the worm. The worm randomly chooses the subject and body of the email message.

This variant is slightly different from other variants. It does not use the iframe exploit, and it does not have the screensaver function.

Antivirus Protection Dates

  • Initial Rapid Release version December 16, 2002
  • Latest Rapid Release version December 16, 2002
  • Initial Daily Certified version December 16, 2002
  • Latest Daily Certified version December 16, 2002
  • Initial Weekly Certified release date December 18, 2002

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Kaoru Hayashi

Discovered: December 16, 2002
Updated: February 13, 2007 11:41:36 AM
Also Known As: I-WORM.Lentin.h [KAV]
Type: Worm
Systems Affected: Windows


When W32.Yaha.H@mm runs, it does the following:

It copies itself as:

  • %system%\Winreg.exe
  • %system%\Msnmsg32.exe
  • %system%\Nav32.exe

NOTE: %system% is a variable. The worm locates the System folder and copies the files to that location. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

It adds the value

winReg %system%\Winreg.exe

to the registry keys

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunService

It modifies the (Default) value

from

"%1" %*

to

%SystemDir%\Nav32.exe" %1 %*

in the registry key

HKEY_LOCAL_MACHINE\Software\Classes\exefile\shell\open\command

Next, it sends itself to all email addresses that it finds in the Windows Address Book, the MSN Messenger List, and the Yahoo Pager list. The email message has the following characteristics:

From: The From field is a randomly selected email address, and it may be spoofed (That is, the name and address in the From field is not really the actual sender).

Subject: W32.Yaha.H@mm randomly chooses the subject from the following strings:

Missing your best friend ?
mAtRiX
Wanna be a hacker ?
Check this
Help someone..
Experience the smooooth music
Still Dreaming..
Pamela 4 U
Friendship ScreenSaver
Are you In Love

Message body:

<HTML><HEAD></HEAD><BODY>
<FONT></FONT>

<<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>>
This e-mail is never sent unsolicited. If you need to unsubscribe,
follow the instructions at the bottom of the message.
***********************************************************

Enjoy this friendship Screen Saver and Check ur friends circle...

Send this screensaver from www.truefriends.net to everyone you
consider a FRIEND, even if it means sending it back to the person
who sent it to you. If it comes back to you, then you'll know youhave a circle of friends.

* To remove yourself from this mailing list, point your browser to:
http://truefriends.net/remove?freescreensaver  
* Enter your email address in the field provided and click "Unsubscribe".

OR...

* Reply to this message with the word "REMOVE" in the subject line.

<<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>> <<<>>>


</BODY></HTML>

Attachme nt: The attachment file name is constructed from one of the following file names:
  • Bestfriend.scr
  • mAtRiX.scr
  • EvilDaemon.scr
  • Love.scr
  • Escort.scr
  • NeverMind.scr
  • HotShot.scr
  • Honey.scr
  • ScreenSaver.scr
  • LoverScreenSaver.scr

followed by one of the following extension pairs:
.pdf            .scr
.gif            .scr
.ppt            .scr
.jpg            .scr
.doc            .scr

Additional functions
It attempts to end antivirus and firewall processes. It searches for active processes, and if the process name is one of the following, it attempts to end the process:
  • NORTON
  • NVC95
  • FP-WIN
  • IOMON98
  • PCCWIN98
  • F-PROT95
  • F-STOPW
  • PVIEW95
  • NAVWNT
  • NAVRUNR
  • NAVLU32
  • NAVAPSVC
  • NISUM
  • SYMPROXYSVC
  • RESCUE32
  • NISSERV
  • VSECOMR
  • VETTRAY
  • TDS2-NT
  • TDS2-98
  • SCAN32
  • PCFWALLICON
  • NSCHED32
  • IAMSERV.EXE
  • FRW.EXE
  • MCAFEE
  • ATRACK
  • IAMAPP
  • LUCOMSERVER
  • LUALL
  • NMAIN
  • NAVW32
  • NAVAPW32
  • VSSTAT
  • VSHWIN32
  • AVSYNMGR
  • AVCONSOL
  • WEBTRAP
  • POP3TRAP
  • PCCMAIN
  • PCCIOMON
  • ESAFE.EXE
  • AVPM.EXE
  • AVPCC.EXE
  • AMON.EXE
  • ALERTSVC
  • ZONEALARM
  • AVP32
  • LOCKDOWN2000
  • AVP.EXE
  • CFINET32
  • CFINET
  • ICMON
  • SAFEWEB
  • WEBSCANX
  • LOCKDOWNADVANCED
  • APACHE.EXE
  • ANTIVIR


Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • 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.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a 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.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. 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.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

Writeup By: Kaoru Hayashi

Discovered: December 16, 2002
Updated: February 13, 2007 11:41:36 AM
Also Known As: I-WORM.Lentin.h [KAV]
Type: Worm
Systems Affected: Windows


NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

To remove the worm:

  • If the worm has not run, and your Symantec antivirus product detects W32.Yaha.H@mm either in an email message or when the worm attempts to run, simply delete it.
  • If the worm has run, you must do the following:
    1. Download updated virus definitions using the Intelligent Updater, but do not install them.
    2. Restart the computer in Safe mode.
    3. Copy Regedit.exe to Regedit.com.
  1. Edit the registry, and reverse the changes that the worm made.
    1. Restart the computer in normal mode.
    2. Start your Symantec antivirus software. If it does not start or function properly, reinstall it.
    3. Install the Intelligent Updater virus definitions that you downloaded in step 1.
    4. Run a full system scan, and delete files that are detected as W32.Yaha.H@mm.

    Detailed instructions for these steps follow.

1. Download virus definitions
2. Restart the computer in Safe mode
    1. Shut down the computer, and turn off the power. Wait 30 seconds. Do not skip this step.
    2. All Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document How to start the computer in Safe mode.

3. To copy Regedit.exe to Regedit.com:
    Because the worm modified the registry so that you cannot run .exe files, you must first make a copy of the Registry Editor as a file with a .com extension and then run that file.
    1. Do one of the following, depending on which operating system you are running:
      • Windows 95/98: Click Start, point to Programs, and click MS-DOS Prompt. This opens a DOS window at the C:\Windows prompt. Proceed to step 2 of this section.
      • Windows Me: Click Start, point to Programs, point to Accessories, and then click MS-DOS Prompt. This opens a DOS window at the C:\Windows prompt. Proceed to step 2 of this section.
      • Windows NT/2000:
        1. Click Start, and click Run.
        2. Type the following, and then press Enter:

          command

          A DOS window opens.
        3. Type the following, and then press Enter:

          cd \winnt
        4. Proceed to step 2 of this section.
      • Windows XP:
        1. Click Start, and click Run.
        2. Type the following, and then press Enter:

          command

          A DOS window opens.
        3. Type the following lines (press Enter after typing each one):

          cd\
          cd \windows
        4. Proceed to step 2 of this section.
    2. Type the following, and then press Enter:

      copy regedit.exe regedit.com
    3. Type the following, and then press Enter:

      start regedit.com

      The Registry Editor opens in front of the DOS window. After you finish editing the registry, exit the Registry Editor, and then exit the DOS window.
  1. Proceed to the next section, "To edit the registry and reverse the changes that the worm made" only after you have accomplished the previous steps.

4. To edit the registry and reverse the changes that the worm made:

    CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.
    1. Navigate to and select the following key:

      HKEY_LOCAL_MACHINE\Software\Classes\exefile\shell\open\command

      CAUTION: The HKEY_LOCAL_MACHINE\Software\Classes key contains many subkey entries that refer to other file extensions. One of these file extensions is .exe. Changing this extension can prevent any files ending with an .exe extension from running. Make sure that you browse all the way along this path until you reach the \command subkey.

      Modify the HKEY_LOCAL_MACHINE\Software\Classes\exefile\shell\open\command subkey that is shown in the following figure:

      <<=== NOTE: Modify this key.
    2. In the right pane, double-click the (Default) value.
    3. Delete the current value data, and then type: "%1" %* (That is, type the following characters: quote-percent-one-quote-space-percent-asterisk.)

      NOTES:
      • On Windows 95/98/Me and Windows NT, the Registry Editor automatically encloses the value within quotation marks. When you click OK, the (Default) value should look exactly like this:

        ""%1" %*"  
      • On Windows 2000/XP, the additional quotation marks will not appear. When you click OK, the (Default) value should look exactly like this:

        "%1" %*
      • Make sure that you completely delete all value data in the command key before you type the correct data. If you leave a space at the beginning of the entry, any attempt to run program files will result in the error message, "Windows cannot find .exe." If this happens to you, start over at the beginning of this document, and make sure that you completely remove the current value data.
    4. Navigate in turn to each of the following keys:

      HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
      HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunService

      NOTE: The RunServices key may not exist on all systems.
    5. In the right pane, delete the value

      winReg     C:\%system%\winReg.exe
    6. Restart the computer.

5. To restart the computer in normal mode:
    Shut down the computer and wait 30 seconds. Restart the computer as you normally would, and allow it to go into normal mode.

6. To start your Symantec antivirus software:
    Start your Symantec antivirus program either from the shortcut icon on your Windows desktop or from the Start menu. If it does not start, or if you have any problems when running the scan in step 8, reinstall the software from your installation files or from the CD.

7. To install the Intelligent Updater virus definitions:
    Double-click the file that you downloaded in Step 1. Click Yes or OK if you are prompted.

8. To scan for and delete the infected files:

Writeup By: Kaoru Hayashi