Analysis by: Karl Dominguez

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan is a component of TROJ_ROOTER.DRL that infects the boot records of the affected system. It writes the said malware in the last sector of the hard disk. It then modifies the master boot record (MBR) to enable the malware to automatically load even before the operating system boots up.

This Trojan arrives as a component bundled with malware/grayware packages. It may be dropped by other malware.

  TECHNICAL DETAILS

File Size: 41,984 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 22 Sep 2011
Payload: Terminates processes

Arrival Details

This Trojan arrives as a component bundled with malware/grayware packages.

It may be dropped by the following malware:

  • TROJ_ROOTER.DRL

Installation

This Trojan drops the following files:

  • %User Temp%\{random characters}.sys - RTKT_RAMNIT.A

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

Autostart Technique

This Trojan registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service
Type = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service
Start = "4"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service
ErrorControl = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service
ImagePath = "%User Temp%\{random characters}.sys"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service
DisplayName = "Micorsoft Windows Service"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service
DeleteFlag = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service\Security
Security = "{hex values}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service\Enum
0 = "Root\LEGACY_MICORSOFT_WINDOWS_SERVICE\0000"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service\Enum
Count = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Micorsoft Windows Service\Enum
NextInstance = "1"

Process Termination

This Trojan terminates the following services if found on the affected system:

  • RapportMgmtService

NOTES:

It is a component of TROJ_ROOTER.DRL that infects the boot records of the affected system. It writes the said malware in the last sector of the hard disk. It then modifies the master boot record (MBR) to enable the malware to automatically load even before the operating system boots up.

  SOLUTION

Minimum Scan Engine: 9.200

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Restore your system's Master Boot Record (MBR)

To restore your system's Master Boot Record (MBR):

• On Windows 2000, XP, and Server 2003:

  1. Insert your Windows Installation CD into your CD drive then restart your computer.
  2. When prompted, press any key to boot from the CD.
  3. On the Main Menu, type r to enter the Recovery Console.
    (Note for Windows 2000: After pressing r, type c to choose the Recovery Console on the repair options screen.)
  4. Type the number that corresponds to the drive and folder that contains Windows (usually C:\WINDOWS) and press Enter.
  5. Type your Administrator password and press Enter.
  6. In the input box, type the following then press Enter:
    fixmbr {affected drive}
  7. Type exit and press Enter to restart the system normally.

• On Windows Vista and 7:

  1. Insert your Windows Installation DVD into the DVD drive, then press the restart button on your computer.
  2. When prompted, press any key to boot from the DVD.
  3. Depending on your Windows Installation DVD, you might be required to choose the installation language. On the Install Windows window, choose your language, locale, and keyboard layout or input method. Click Repair your computer.
  4. Select Use recovery tools that can help fix problems starting Windows. Select your installation of Windows. Click Next.
  5. If the Startup Repair window appears, click Cancel, Yes, then Finish.
  6. In the System Recovery Options menu, click Command Prompt.
  7. In the Command Prompt window, type the following then press Enter:
    BootRec.exe /fixmbr
  8. Type exit and press Enter to close the Command Prompt window.
  9. Click Restart to restart your computer normally.

Step 3

Remove the malware/grayware file that dropped/downloaded TROJ_RAMNIT.SMUT

    TROJ_ROOTER.DRL

Step 4

Remove the malware/grayware file dropped/downloaded by TROJ_RAMNIT.SMUT

     RTKT_RAMNIT.A

Step 5

Delete this registry key

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • Micorsoft Windows Service

Step 6

Scan your computer with your Trend Micro product to delete files detected as TROJ_RAMNIT.SMUT. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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