Summary

Isras worm appeared in the beginning of July 2003. The worm spreads in e-mail with different, subjects, bodies and attachments. The worm also spreads via Kazaa file sharing network.

Additional Details

The worm's file is a Windows PE executable 147kb long written in Visual Basic. The worm's file is not compressed. The worm contains 2 embedded files in its body.

Installation to system

When the worm's file is run by a user, it installs itself to system. It copies itself several times and drops a few files:

 %winsysdir%\ossmtp.dll - the SMTP library used to spread the worm
 %winsysdir%\vUser.exe
 %winsysdir%\vShell.exe - copy of the worm's file
 %winsysdir%\Win32.exe - copy of the worm's file
 %tempdir%\faq.exe - copy of the worm's file used for spreading
 %tempdir%\fun.exe
 %tempdir%\support.exe - copy of the worm's file used for spreading
 %tempdir%\toolbar.exe - copy of the worm's file used for spreading
 %tempdir%\update.exe - copy of the worm's file used for spreading
 %tempdir%\wizard.exe - copy of the worm's file used for spreading
 %tempdir%\q322593.exe - copy of the worm's file used for spreading

where %tempdir% represents a temporary folder and %winsysdir% represents Windows System directory.

The worm modifies the default text file startup key:

 [HKEY_CLASSES_ROOT\txtfile\shell\open\command]
 @ = "%winsysdir%\vshell.exe %1"

Also the worm creates a startup key for one of its files:

 [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run]
 "Win32" = ""%winsysdir%\win32.exe"

This modification makes the worm's file run during every Windows session.

Spreading in e-mails

The worm spreads in e-mail messages with different subjects, bodies and attachments. The worm gets victims' e-mail addresses from Windows Address Book and sends itself to all found addresses. The worm sends the following messages:

From:

 update@microsoft.com

Subject:

 Windows Update

Body:

 Your file is attached to message.
 For more information go to Windows Update http://windowsupdate.microsoft.com

Attachment:

 update.exe

OR

From:

 update@microsoft.com

Subject:

 PS1

Body:

 Your file is attached to message.
 For more information go to Windows Update http://windowsupdate.microsoft.com

Attachment:

 q322593.exe

OR

From:

 help@google.com

Subject:

 Update Your ToolBar

Body:

 Your file is attached to message.
 For more information go to Google home page http://www.google.com

Attachment:

 toolbar.exe

OR

From:

 help@google.com

Subject:

 Auto Search Wizard

Body:

 Your file is attached to message.
 For more information go to Google home page http://www.google.com

Attachment:

 wizard.exe

OR

From:

 copyright@yahoo-inc.com

Subject:

 Yahoo FAQ

Body:

 Your file is attached to message.
 For more information go to Yahoo home page http://www.yahoo.com

Attachment:

 faq.exe

OR

From:

 copyright@yahoo-inc.com

Subject:

 Support For Search

Body:

 Your file is attached to message.
 For more information go to Yahoo home page http://www.yahoo.com

Attachment:

 support.exe

The worm does not use any tricks to make its attachment start automatically on recipients' systems.

Spreading in Kazaa file sharing network

The worm tries to locate Kazaa P2P (peer-to-peer) file sharing client and copy itself there with one of the following names:

 XP Keys.exe
 OfficeXP Keys.exe
 NAV_2003 Crack.exe
 Doom_3 Crack.exe
 GTA Vice City Crack.exe

If a Kazaa user downloads and runs any of these files, his computer becomes infected with the worm.

Payload

The worm tries to disable Symantec's security and anti-virus software by modifying the special Registry key and by unregistering certain software components.

Also the worm searches local hard disks for *.URL files and replaces links in them with one the following:

 http://www.ynet.co.il/
 http://www.tapuz.co.il/
 http://www.nana.co.il/
 http://www.msn.co.il/
 http://www.walla.co.il/

Detection

Detection of Israz worm is available in the following FSAV updates:

[FSAV_Database_Version]

Version=2003-07-10_01

[Description: Alexey Podrezov; F-Secure Corp.; July 10th, 2003]