Analysis by: Mar Philip Elaurza
ALIASES:

Win32/TrojanDownloader.Wauchos.AK (ESET-NOD32), Trojan.Win32.Inject.viav (Kaspersky), Trojan-FHDS!D2D09C47D187 (McAfee), VirTool:Win32/Obfuscator.APL (Microsoft),

 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: Spammed via email

This backdoor arrives as attachment to mass-mailed email messages.

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

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size: 170,810 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 29 Sep 2015
Payload: Steals information, Compromises system security

Arrival Details

This backdoor arrives as attachment to mass-mailed email messages.

Installation

This backdoor drops the following files:

  • %User Temp%\cdo{random numbers}.dll

(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 the following copies of itself into the affected system:

  • %All Users Profile%\ms{random}.exe

(Note: %All Users Profile% is the All Users folder, where it usually is C:\Documents and Settings\All Users on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\ProgramData 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 processes:

  • msiexec.exe

It injects itself into the following processes as part of its memory residency routine:

  • explorer.exe
  • created msiexec.exe

Autostart Technique

This backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run
{random number} = "%All Users Profile%\ms{random}.exe"

Other System Modifications

This backdoor modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = "2"

(Note: The default value data of the said registry entry is 1.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = "0"

(Note: The default value data of the said registry entry is 1.)

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Download a file directed by C&C server, save it as %User Temp%\KB{8 random numbers}.exe and execute it
  • Download a file directed by C&C server, save it as %All User Profile%\ms{random number}.dat and load it
  • Download a file directed by C&C server, save it as %All User Profile%\ms{random}.exe:{random number}
  • Copy %System%\cdosys.dll to %User Temp%\cdo{random number}.dll and load it
  • Start a process
  • Uninstall itself
  • Perform remote shell commands
  • Restart system

(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.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

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

  • http://{BLOCKED}ve.com/larry.php
  • http://{BLOCKED}s.su/monkey.php
  • http://{BLOCKED}rf.net/amazon.php
  • http://{BLOCKED}ate.com/sales.php

Information Theft

This backdoor gathers the following data:

  • Operating system information
  • Local IP address
  • Root volume serial number

Other Details

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

  • update.microsoft.com
  • microsoft.com
  • google.com
  • bing.com
  • yahoo.com

It does the following:

  • Checks if it is being run in a virtual environment or emulation software. If so, it will perform infinite sleep.
  • Checks if there is a running network monitoring software in the affected machine. If found, it will perform infinite sleep.
  • Connects to the following Network Time Protocol (NTP) servers:
    • {BLOCKED}ol.ntp.org
    • {BLOCKED}rica.pool.ntp.org
    • {BLOCKED}eania.pool.ntp.org
    • {BLOCKED}ia.pool.ntp.org
    • {BLOCKED}uth-america.pool.ntp.org
    • {BLOCKED}rth-america.pool.ntp.org
    • {BLOCKED}rope.pool.ntp.org

It deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.938.04
FIRST VSAPI PATTERN DATE: 24 Sep 2015
VSAPI OPR PATTERN File: 11.939.00
VSAPI OPR PATTERN Date: 25 Sep 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

Delete this 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\CurrentVersion\policies\Explorer\Run
    • {random number} = "%All Users Profile%\ms{random}.exe"

Step 5

Restore this modified registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator’s help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: Hidden = "2"
      To: Hidden = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: ShowSuperHidden = "0"
      To: ShowSuperHidden = 1

Step 6

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.
  • %All User Profile%\ms{random}.exe
  • %All User Profile%\ms{random number}.dat
  • %User Temp%\KB{8 random numbers}.exe
  • %User Temp%\cdo{random number}.dll

Step 7

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