Analysis by: Michael John Marcos

 ALIASES:

PWS:Win32/Bzub (Microsoft), Win32/Spy.Agent.OAX trojan (ESET), Mal/Buzb-A (Sophos)

 PLATFORM:

Windows

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

  • Threat Type: File infector

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet

This file infector is embedded in an infected zip file served by a website hosted in North Korea.

To get a one-glance comprehensive view of the behavior of this File infector, refer to the Threat Diagram shown below.

This file infector may be unknowingly downloaded by a user while visiting malicious websites.

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: 1,738,811 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 14 Jan 2015
Payload: Connects to URLs/IPs

Arrival Details

This file infector may be unknowingly downloaded by a user while visiting malicious websites.

Installation

This file infector drops the following copies of itself into the affected system:

  • %Application Data%\Microsoft\Messenger\Extension\WdExt.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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 injects itself into the following processes as part of its memory residency routine:

  • explorer.exe
  • iexplore.exe
  • ieuser.exe
  • firefox.exe
  • chrome.exe
  • msimn.exe
  • outlook.exe
  • winmail.exe
  • msnmsgr.exe
  • yahoomessenger.exe
  • ftp.exe

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Windows Defender Extension = "%Application Data%\Microsoft\Defender\launch.exe"

Backdoor Routine

This file infector executes the following commands from a remote malicious user:

  • Execute remote shell
  • List processes
  • List files and folders
  • Download and execute file
  • Upload file
  • Capture Screenshots of affected system

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

  • http://a.{BLOCKED}perl.sh
  • http://a-{BLOCKED}-01.slyip.net
  • http://{BLOCKED}was-01.dyndns.org

It posts the following information to its command and control (C&C) server:

  • Date and Time(UTC)
  • Computer Name
  • Username
  • OS Information
  • MAC Address
  • IP Address and Subnet Mask
  • Adapter Information
  • Network (Internet | Closed)
  • TTL \ Hop Limit
  • Network Type (LAN | RAS | PROXY | MODEM | OFFLINE)

Dropping Routine

This file infector drops the following files:

  • %Application Data%Microsoft\Caches\Files\usd.dll
  • %Application Data%\Microsoft\Common\Shared\dis.dll
  • %Application Data%\Microsoft\Identities\{computer name}\arc.dll
  • %Application Data%\Microsoft\Repairs\sha.dll
  • %Application Data%\Microsoft\Shared\Modules\fil.dll
  • %Application Data%\Microsoft\Windows\Addins\att.dll
  • %Application Data%\Microsoft\Defender\launch.exe
  • %System%\wtime32.dll
  • %System%\mscaps.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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.)

Other Details

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

  • http://windowsupdate.microsoft.com

It deletes the initially executed copy of itself

NOTES:

It disables the Windows error notification functionality.

It infects .exe files in shared folders and removable drives.

It adds the following registry keys to setup its persistence mechanism:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\{ef2b00e3-19da-4e78-b118-6b6451b719f2}
StubPath = ""%System%\mscaps.exe" /s /n /i:U shell32.dll"
ComponentID = "DirectShow"
Version = "1,125,2406,1"
Locale = "*"

  SOLUTION

Minimum Scan Engine: 9.700

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

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry key

[ 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.

  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\{ef2b00e3-19da-4e78-b118-6b6451b719f2}

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Windows Defender Extension = "%Application Data%\Microsoft\Defender\launch.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.
  • %Application Data%\Microsoft\Messenger\Extension\WdExt.exe
  • %Application Data%Microsoft\Caches\Files\usd.dll
  • %Application Data%\Microsoft\Common\Shared\dis.dll
  • %Application Data%\Microsoft\Identities\{computer name}\arc.dll
  • %Application Data%\Microsoft\Repairs\sha.dll
  • %Application Data%\Microsoft\Shared\Modules\fil.dll
  • %Application Data%\Microsoft\Windows\Addins\att.dll
  • %Application Data%\Microsoft\Defender\launch.exe
  • %System%\wtime32.dll
  • %System%\mscaps.exe

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as PE_WINDEX.A-O. 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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