Worm:W32/Zimuse.B

Arrival to the system

Zimuse.B arrives on the system either as a standalone file (possibly from a malicious download or email) or by infected removable devices (e.g., USB sticks).

When the malware is executed, it will install malicious components along with a clean IQTest program and a readme.txt. The Iqtest.exe program is clean and is an actual IQ test program.

The following file operations will be performed on the system:

• Creates these files:
• Uses these temporary files:

Launchpoint/Autostart

Uses registry launchpoints to ensure its components run or are loaded as services on every startup (see below).

Registry Changes

Creates these keys:

• HKLM\System\CurrentControlSet\Services\EventLog\System\MSTART
• HKLM\System\CurrentControlSet\Services\MSTART
• HKLM\System\CurrentControlSet\Services\MSTART\Security
• HKLM\System\CurrentControlSet\Services\Mseu
• HKLM\system\currentcontrolset\services\UnzipService

Sets these values:

• HKLM\System\CurrentControlSet\Services\EventLog\System\MSTART EventMessageFile = %SystemRoot%\System32\Drivers\MSTART.SYS;
• HKLM\System\CurrentControlSet\Services\EventLog\System\MSTART TypesSupported = 7
• HKLM\System\CurrentControlSet\Services\MSTARTType = 1 by %windir%\system32\services.exe (PID:640)
• HKLM\System\CurrentControlSet\Services\MSTART Start = 3
• HKLM\System\CurrentControlSet\Services\MSTART ErrorControl = 1
• HKLM\System\CurrentControlSet\Services\MSTART ImagePath = \??\C:\WINDOWS\system32\Drivers\MSTART.SYS [Launchpoint: Service]
• HKLM\System\CurrentControlSet\Services\MSTART DisplayName = MSTART
• HKLM\System\CurrentControlSet\Services\MSTART\Security Security = by %windir%\system32\services.exe (PID:640)
• HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run [Launchpoint: Run]
• HKLM\System\CurrentControlSet\Services\Mseu Type = 1
• HKLM\System\CurrentControlSet\Services\Mseu Start = 2
• HKLM\System\CurrentControlSet\Services\Mseu ErrorControl = 1
• HKLM\System\CurrentControlSet\Services\Mseu Tag = 1
• HKLM\System\CurrentControlSet\Services\Mseu Group = Extended base
• HKLM\system\currentcontrolset\services\UnzipService Type = 272
• HKLM\system\currentcontrolset\services\UnzipService Start = 2 by %localsettings\Temp\Regini.exe (PID:428)
• HKLM\system\currentcontrolset\services\UnzipService by %localsettings\Temp\Regini.exe (PID:428) [Launchpoint: Service]
• HKLM\system\currentcontrolset\services\UnzipService ErrorControl = 0
• HKLM\system\currentcontrolset\services\UnzipService DisplayName = Self extract service
• HKLM\system\currentcontrolset\services\UnzipService ObjectName = LocalSystem
• HKLM\system\currentcontrolset\services\UnzipService

Description = Self extract archive decrypt

Infection

After a certain time period from the initial infection, the worm will infect removable drives inserted into the system by dropping a copy of itself named zipsetup.exe and an autorun.inf file as shown below:

[autorun] shellexecute=zipsetup.exe /H

Payload

After a further period of dormancy, the worm will trigger its payload, which will overwrite the Master Boot Record of available drives on the system, and effectively crippling the file system and rendering data on the disk inaccessible except with specialist tools. The following dialog box will be displayed:

On reboot the system will be unbootable.

Removal

Manual removal:

1) Use task manager or process explorer to kill the "MSEUS.EXE" process.

2) Delete the following files:

• %windir%\system32\drivers\Mstart.sys
• %programfiles%\Dump\Dump.exe
• %windir%\system32\drivers\Mseu.sys
• %windir%\system32\mseus.exe
• %windir%\system32\tokset.dll
• %windir%\system32\ainf.inf

Delete as well any instances of zipsetup.exe on root folders as well as the autorun.inf

3) Delete the malicious registry entries, especially launchpoints as listed in the description.

4) Reboot system, run full scan.