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VBS_CARBANAK.DXP

January 26, 2017
 Analysis by: Julie Anne Cabuhat
 ALIASES:

VBS:Agent-BRK [Trj] (Avast)

 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:

Dropped by other malware

This backdoor may be dropped by other malware.

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

  TECHNICAL DETAILS

File Size:

194,298 bytes

File Type:

VBS

Memory Resident:

Yes

Initial Samples Received Date:

03 Jan 2017

Payload:

Connects to URLs/IPs, Collects system information, Executes files

Arrival Details

This backdoor may be dropped by the following malware:

  • TROJ_CARBANAK.DXP

Installation

This backdoor drops the following file(s)/component(s):

  • %User Temp%\WindowsUpdate_X24532\MyIniFile.ini
  • %User Temp%\WindowsUpdate_X24532\screenshot-cmd.ps1
  • %User Temp%\WindowsUpdate_X24532\box.txt
  • %User Temp%\WindowsUpdate_X24532\beginer.vbs
  • %User Temp%\WindowsUpdate_X24532\runnerr.vbs
  • %User Temp%\WindowsUpdate_X24532\loader.vbs
  • %User Temp%\WindowsUpdate_X24532\autostarter2.vbs
  • %User Temp%\WindowsUpdate_X24532\checkcomp.vbs
  • %User Temp%\WindowsUpdate_X86532\ggldr.vbs
  • %User Temp%\WindowsUpdate_X86532\start.vbs
  • %User Temp%\WindowsUpdate_X24532\Foxconn.lnk
  • %User Temp%\WindowsUpdate_X86532\Foxconn.lnk
  • %User Temp%\WindowsUpdate_X32794\begCobal.vbs
  • %User Temp%\WindowsUpdate_X32794\updateSys.ps1
  • {malware path}\out.txt

(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 creates the following folders:

  • %User Temp%\WindowsUpdate_X24532
  • %User Temp%\WindowsUpdate_X86532
  • %User Temp%\WindowsUpdate_X32794

(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.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
UpdateWindowsTmp0_ = explorer.exe %User Temp%\WindowsUpdate_X24532\Foxconn.lnk

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
UpdateWindowsTmp1_ = explorer.exe %User Temp%\WindowsUpdate_X86532\Foxconn.lnk

Backdoor Routine

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

  • List running processes
  • Acquire the following computer information:
    • Operating System Name
    • Operating System version
    • Service Pack Major and Minor Version
    • Operating System Manufacturer
    • Windows Directory
    • Operating System Locale
    • Available Physical Memory
    • Total Virtual Memory
    • Available Virtual Memory
    • Size stored in paging files
    • Computer System Name
    • Computer System Manufacturer
    • Computer System Model
    • Current Time Zone
    • Total Physical Memory
    • Processor Information
    • BIOS Version
    • User Domain
    • User Name
    • Microsoft Office applications and version
  • Capture and send screenshots
  • Run VBS scripts
  • Run executable files
  • Run powershell scripts
  • Run cmd commands
  • Uninstall itself
  • Update itself

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

  • http://{BLOCKED}r.com/css/informs.jsp
  • https://docs.{BLOCKED}e.com/forms/d/e/1FAIpQLSfzZjWELySdnVvjcM63JOEk4nr3ZdPPXlBcTmWAi-loa0of9g/formResponse
  • https://{BLOCKED}t.{BLOCKED}e.com/macros/s/AKfycbxGIvnr9iMU-a16PIrgp2pxWk-mxF-CAvqFR0DCDUYX8PIA03Aw/exec

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

  • Operating System Name
  • Operating System version
  • Service Pack Major and Minor Version
  • Operating System Manufacturer
  • Windows Directory
  • Operating System Locale
  • Available Physical Memory
  • Total Virtual Memory
  • Available Virtual Memory
  • Size stored in paging files
  • Computer System Name
  • Computer System Manufacturer
  • Computer System Model
  • Current Time Zone
  • Total Physical Memory
  • Processor Information
  • BIOS Version
  • User Domain
  • User Name
  • Running processes
  • Microsoft Office applications and version

NOTES:
The backdoor uses various Google services such as Google Apps Script and Google Forms for its communication.

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

13.180.06

FIRST VSAPI PATTERN DATE:

25 Jan 2017

VSAPI OPR PATTERN File:

13.181.00

VSAPI OPR PATTERN Date:

26 Jan 2017

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • UpdateWindowsTmp0_ = "explorer.exe %User Temp%\WindowsUpdate_X24532\Foxconn.lnk"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • UpdateWindowsTmp1_ = "explorer.exe %User Temp%\WindowsUpdate_X86532\Foxconn.lnk"

Step 5

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %User Temp%\WindowsUpdate_X24532
  • %User Temp%\WindowsUpdate_X86532
  • %User Temp%\WindowsUpdate_X32794

Step 6

Search and delete these files

[ 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.
  • {malware path}\out.txt

Step 7

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