BKDR_EMDIVI.MSB

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It does not have any propagation routine.

It runs certain commands that it receives remotely from a malicious user. Doing this puts the affected computer and information found on the computer at greater risk.

It retrieves specific information from the affected system.

Arrival Details

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This backdoor drops the following files:

• %User Temp%\vmat.exe ← detected also as BKDR_EMDIVI.MSB

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It drops and executes the following files:

• %User Temp%\20150320.pdf ← decoy file

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

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

• 71dc950644302515373f6af33cbc9edf

Autostart Technique

This backdoor creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
vmat = "%User Temp%\vmat.exe"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "%System%\userinit.exe,%User Temp%\vmat.exe,"

(Note: The default value data of the said registry entry is "%System%\userinit.exe,".)

It drops the following file(s) in the Windows User Startup folder to enable its automatic execution at every system startup:

• %Common Startup%\vmat.lnk
• %User Startup%\vmat.lnk

(Note: %Common Startup% is the system's shared Startup folder, which is usually C:\Documents and Settings\All Users\Start Menu\Programs\Startup on Windows 2000, XP, and Server 2003, and C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup on Windows Vista, 7, and 8.. %User Startup% is the current user's Startup folder, which is usually C:\Documents and Settings\{user}\Start Menu\Programs\Startup on Windows 2000 and XP, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup on Windows Vista, 7, and 8.)

Propagation

This backdoor does not have any propagation routine.

Backdoor Routine

This backdoor executes the following command(s) from a remote malicious user:

• Enumerate files and folders
• Delete files and folders
• Download files
• Upload files
• Execute files
• Get file attributes
• Enumerate processes
• Perform remote shell
• Loads a library using LoadLibrary API
• Import functions from a library using GetProcAddress API
• Gather credentials using CredEnumerate or PStoreCreateInstance API
• Gather Firefox settings from prefs.js
• Gather proxy settings from proxy.pac
• Gather proxy settings from windows registry
• Sleep

It connects to the following URL(s) to send and receive commands from a remote malicious user:

• http://www.{BLOCKED}e.co.jp/home/common/index.php
• http://hi.{BLOCKED}sakura.com/www/index.php

Information Theft

This backdoor retrieves the following information from the affected system:

• Host name
• Process ID of the malware
• Memory Size (RAM)
• Internet Explorer Version
• Windows OS Version
• System Language
• Location
• Time Zone Information

Other Details

This backdoor connects to the following URL(s) to check for an Internet connection:

• http://www.msftncsi.com/ncsi.txt
• http://www.microsoft.com/en-us/default.aspx
• http://www.yahoo.co.jp

NOTES:

It will not execute properly if the hostname was similar to the following strings:

• wilbert-SC1508
• xp-sp3-template
• mip-xp-cht
• CWS01_03
• wilbert-SC2202
• CWS05D102

It enumerates all visible windows and compares each window's title bar text with the following strings:

• OllyDbg
• W32Dasm
• Wireshark
• SoftICE
• Process Explorer
• Process Monitor
• Process Hacker

If a window's title bar text contains any of the said strings, it will pause the execution of its malicious routine by performing a Sleep command.

It uses a Adobe Acrobat Reader icon and drops a non-malicious file 20150320.pdf. It will then open the file 20150320.pdf to deceive users that it is a normal file.

It does not have rootkit capabilities.

It does not exploit any vulnerability.