W32.Yarner.A@mm

SUMMARY

Due to a low submission rate, Symantec Security Response is downgrading this threat to a Category 2.

W32.Yarner.A@mm is a mass-mailing worm. The worm sends itself to email addresses that it finds in the Microsoft Outlook address book and in local files.

The worm uses the system-configured or hardcoded SMTP server to send messages with the subject Trojaner-Info Newsletter, followed by the current date. The message body is in German and the attachment name is Yawsetup.exe.

In addition, the worm may attempt to delete all files on the computer.

Protection

• Initial Rapid Release version February 19, 2002
• Latest Rapid Release version July 12, 2008 revision 018
• Initial Daily Certified version February 19, 2002
• Latest Daily Certified version July 12, 2008 revision 019
• Initial Weekly Certified release date February 19, 2002

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

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: High

Distribution

• Distribution Level: High

TECHNICAL DETAILS

When it is executed, W32.Yarner.A@mm does the following:

It copies itself to \%Windows%\Notepad.exe, which overwrites the Notepad program.

NOTES:

• %Windows% is a variable. The worm locates the \Windows folder (by default this is C:\Windows or C:\Winnt) and copies itself to that location.
• Before the worm overwrites Notepad.exe, it saves a copy of the file as %Windows\Notedpad.exe. (Notice the slight change in the file names: The new, infected file is now Notepad.exe, while the original, uninfected file has be renamed to Notedpad.exe--the letter d was added after "Note".)

As a result, when Notepad.exe is opened, the worm executes and attempts to launch the original (renamed) Notepad program.

In addition, the worm copies itself to %Windows%\<random characters>.exe

It also adds the associated value

<random characters>        <random characters>.exe

to the registry key

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Runonce

This causes the worm to run the nest time that you start Windows.

The worm uses MAPI to send itself as to email addresses that it finds in the Microsoft Outlook address book and by searching files that have the extensions .php, .htm, .shtm, .cgi, or .pl. The worm pretends to be a new version of the YAW application that was released by Trojaner Info in Germany.

The message has the following characteristics:

Attachment: Yawsetup.exe

Subject: Trojaner-Info Newsletter <Current Date>

Message:

Hallo !

Willkomen zur neuesten Newsletter-Ausgabe der Webseite Trojaner-Info.de.
Hier die Themen im Ueberblick:

01. YAW 2.0 - Unser Dialerwarner in neuer Version

************************************
01. YAW 2.0 - Unser Dialerwarner in neuer Version

Viele haben ihn und viele moegen ihn - unseren Dialerwarner YAW. YAW ist
nun in einer brandneuen und stark erweiterten Version verfuegbar. Alle unsere
Newsletterleser bekommen ihn kostenlos zusammen mit diesem Newsletter.
Also einfach die angehaengte Datei starten und YAW 2.0 installieren. Bei Fragen
steht Ihnen der Programmierer des bislang einzigartigen Programmes Andreas Haak
unter andreas@ants-online.de zur Verf
gung. Viel Spaß mit YAW!

<http:/ /www.trojaner-info.de/dialer/yaw.shtml>

************************************

Das war die heutige Ausgabe mit den aktuellsten Trojaner-Info News. Wir
bedanken uns fuer eure Aufmerksamkeit und wuenschen allen Lesern noch eine
angenehme Woche.

Mit freundlichem Gruss

Thomas Tietz & Andreas Ebert
<http:/ /www.trojaner-info.de>

************************************
Anzahl der Subscriber: 5.966
Durchschnittliche Besuchzahl/Tag: 4.488
Diese Mail ist kein Spam ! Diesen Newsletter hast du erhalten, da du in unserer
Verteilerliste aufgenommen wurdest. Solltest du unseren Newsletter nicht selber
abonniert haben, sondern eine andere Person ohne dein Wissen, kannst du
diesen auf unseren Seiten wieder abbestellen. Oder sende uns einfach eine
entsprechende E-Mail.

************************************

The worm also creates the following files:

• %Windows%\Kernei32.daa
• %Windows%\kernei32.das

These files are not viral; instead, they store server and address information that is used by the virus.

Finally, depending on a random counter, the worm may delete all files on the drive on which Windows is installed.

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.

REMOVAL

If this worm has been executed, it is possible that all files have been deleted from the hard drive. If this is the case, you must a fully reinstall of the system.

If the worm has not deleted all files, delete files that are detected as W32.Yarner.A@mm, rename Notedpad.exe to Notepad.exe, and remove the value that the worm added to the registry.

To remove the worm:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine if definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
   • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine if definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
     
     Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
     
2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
3. Run a full system scan.
4. Delete all files that are detected as W32.Yarner.A@mm.

To rename Notedpad:

1. Using Windows Explorer, locate the file \%Windows%\Notedpad.exe.
   
   NOTE: %Windows% is a variable. The file will be in the folder in which Windows is installed. By default, this is C::\Windows or C:\Winnt.
   
2. Right-click the Notedpad.exe file, and click Rename.
3. Rename the file back to Notepad.exe.

To edit the registry:

CAUTION: We strongly recommend 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 back up the Windows registry for instructions.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the following key:
   
   HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Runonce
   
4. In the right pane, look for a value that consists of a string of random characters.
5. Select this value and delete it.
6. Click Registry, and click Exit.