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Worm:W32/Zimuse.B

First posted on 27 January 2010.
Source: SecurityHome

Aliases :

Worm:W32/Zimuse.B is also known as Win32/Zimuse.B (Other), Worm:Win32/Zumes.A!sys (Microsoft).

Explanation :

A standalone malicious program which uses computer or network resources to make complete copies of itself. May include code or other malware to damage both the system and the network.

Additional DetailsGeneral information
Zimuse is a family of worms that performs destructive overwrite of the Master Boot Record of disk drives on the infected system.

Arrival to the system
Zimuse.B arrives on the system either as a standalone file (possibly from a malicious download or e-mail) 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:

€ %windir%\system32\drivers\Mstart.sys [Worm.Zimuse.A] € %programfiles%\Dump\Dump.exe [nonmalicious component] € %windir%\system32\drivers\Mseu.sys [Worm.Zimuse.A] € %windir%\system32\mseus.exe [Worm.Zimuse.A] € %windir%\system32\tokset.dll [copy of itself] € %windir%\system32\ainf.inf [copy of the autorun.inf file] € c:\IQTEST\Iqtest.exe [clean IQTest program] € c:\IQTEST\Readme.txt [clean text file]

€ Uses these temporary files:

€ %temp%\Regini.exe € %temp%\Dump.ini € %temp%\Mseu.ini € %temp%\mseus.ini € %temp%\Instdrv.exe

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\MSTART

Type = 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.

Last update 27 January 2010

 

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