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TROJ_KILLMBR.DF
Aliases: Trojan Horse (Symantec), W32/INJECTO.MBF!tr (Fortinet), Trojan.Win32.Spy (Ikarus)
Malware type: Trojan
Destructive: No
Platform: Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)
Encrypted: No
In the wild: Yes

Overview


This Trojan arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

Technical Details


File size: 241,664 bytes
File type: EXE
Memory resident: No
Initial samples received date: 20 Mar 2013

Arrival Details

This Trojan arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

Installation

This Trojan drops the following non-malicious files:

  • mp.swf
  • 1f.mp3
  • 24mhk04.gif
  • 25z18pg.jpg

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • MICRO_ESENCIAL0192301

Other System Modifications

This Trojan modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Session Manager\Memory Management
ClearPageFileAtShutdown = "1"

(Note: The default value data of the said registry entry is 0.)

File Infection

This Trojan searches for files with the following extension names and overwrites these files with its code:

  • .html
  • .htm
  • .aspx
  • .asp
  • .jsp
  • .do
  • .php

Process Termination

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

  • SENS
  • Alerter

NOTES:

The overwritten files are detected as HTML_DFACE.A. This is the detection for the webpage displayed notifying the user that their systems are infected by this malware.

The dropped non-malicious files are used by HTML_DFACE.A to display its full contents. These files are dropped in each directory where a file is overwritten.

The overwritten files can not be recovered unless there is a backup.

It corrupts the MBR by writing garbage code taken from the Interrupt Vector Table and forces the boot to enter an infinite loop.

Solution


Minimum scan engine: 9.300
First VSAPI Pattern File: 9.818.07
First VSAPI Pattern Release Date: 20 Mar 2013
VSAPI OPR Pattern Version: 9.819.00
VSAPI OPR Pattern Release Date: 20 Mar 2013

Step 1

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:
    BoorRec.exe /fixmbr
  8. Type exit and press Enter to close the Command Prompt window.
  9. Click Restart to restart your computer normally.

Step 2

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

Step 3

Restore this modified registry value

[ 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\Control\Session Manager\Memory Management
    • From: ClearPageFileAtShutdown = "1"
      To: ClearPageFileAtShutdown = 0

Step 4

Search and delete these files

[ Learn more ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • mp.swf
  • 1f.mp3
  • 24mhk04.gif
  • 25z18pg.jpg

Step 5

Scan your computer with your Trend Micro product to delete files detected as TROJ_KILLMBR.DF. 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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Analysis By: Anthony Joe Melgarejo

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