Analysis by: Sammy Chua




  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes


Infection Channel: Dropped by other malware, Downloaded from the Internet

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 executes commands from a remote malicious user, effectively compromising the affected system.

It gathers certain information on the affected computer.


File Size: 221,184 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 11 Jul 2015
Payload: Connects to URLs/IPs, Compromises system security, Steals information

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.


This backdoor drops and executes the following files:

  • %User Temp%\vmater.exe -> detected as BKDR_EMDIVI.YUR
  • %User Temp%\270529.docx -> decoy document

(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:

  • 72af4f0cadebcad7d7443a2c72859c0a

Autostart Technique

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

Windows NT\CurrentVersion\Winlogon
Userinit = "%System%\userinit.exe,%User Temp%\vmater.exe,"

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

  • %User Startup%\vmater.lnk -> pointed to vmater.exe
  • %Common Startup%\vmater.lnk -> pointed to vmater.exe

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.. %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.)


This backdoor does not have any propagation routine.

Backdoor Routine

This backdoor executes the following commands 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}
  • http://www.{BLOCKED}
  • http://may.{BLOCKED}

As of this writing, the said sites are inaccessible.

Information Theft

This backdoor gathers the following information on the affected computer:

  • Host name
  • Process ID of the malware
  • Internet Explorer Version
  • OS Information (Major Version, Minor Version and Build Number)
  • System Language
  • Country/Region
  • Time Zone Information

Other Details

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



It does not execute properly if the hostname is 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 pauses the execution of its malicious routine by performing a Sleep command.

It uses a Microsoft Word document icon then drops and opens a non-malicious file %User Temp%\270529.docx to deceive users that it is a normal file.

It does not have rootkit capabilities.

It does not exploit any vulnerability.


Minimum Scan Engine: 9.750
VSAPI OPR PATTERN File: 11.713.00
VSAPI OPR PATTERN Date: 06 Jun 2015

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

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\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Userinit = "%System%\userinit.exe,%User Temp%\vmater.exe,"
      To: Userinit = %System%\userinit.exe,

Step 5

Search and delete this file

[ 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.
  • %User Temp%\vmater.exe
  • %User Temp%\270529.docx
  • %User Startup%\vmater.lnk
  • %Common Startup%\vmater.lnk

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_EMDIVI.YUR. 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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