Analysis by: Sammy Chua
ALIASES:

Troj/Emdivi-A (Sophos); HEUR:Trojan.Win32.Generic (Kaspersky); Backdoor.Emdivi!gen1 (Symantec)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: 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.

  TECHNICAL DETAILS

File Size: 219,136 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 18 Jun 2015
Payload: Connects to URLs/IPs, 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.

Autostart Technique

This backdoor 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,{malware file path}\{malware file name},"

Propagation

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}eworld.jp/feeds.php
  • http://www.{BLOCKED}norei.com/blog/index.php

As of this writing, the said sites are inaccessible.

Information Theft

This backdoor gathers the following data:

  • 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:

  • http://www.microsoft.com
  • http://www.msftncsi.com
  • http://www.yahoo.co.jp

NOTES:

This backdoor does not execute properly if the hostname is similar to the following strings:

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

It enumerates all visible windows and compares each window's title bar text to 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 does not have rootkit capabilities.

It does not exploit any vulnerability.

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.738.06
FIRST VSAPI PATTERN DATE: 18 Jun 2015
VSAPI OPR PATTERN File: 11.739.00
VSAPI OPR PATTERN Date: 19 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
    • Userinit = "%System%\userinit.exe,{malware file path}\{malware file name}, "

Step 5

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