Analysis by: Alyssa Christelle Ramos
ALIASES:

VBS.Downloader.Trojan(NORTON)

 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 gathers certain information on the affected computer.

  TECHNICAL DETAILS

File Size: 78,578 bytes
File Type: VBS
Memory Resident: Yes
Initial Samples Received Date: 29 Nov 2017
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.

Installation

This Backdoor uses the following names for the copies it drops:

  • %Common Startup%\{25 Random Characters}.vbs
  • %Application Data%\g_{25 Random Characters}.vbs_w.vbs
  • %Application Data%\{25 Random Characters}.vbs
  • %Application Data%\1192431963351_log.txt

(Note: %Common Startup% is the startup folder for all users, which is usually C:\Documents and Settings\All Users\Start Menu\Programs\Startup on Windows 2000, XP, and Server 2003, or C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup on Windows Vista, 7, and 8.. %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

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\Policies\
Explorer\Run
{25 Random Characters} = wscript.exe //B "%Application Data%\{25 Random Characters}.vbs

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
{25 Random Characters} = wscript.exe //B "%Application Data%\{25 Random Characters}.vbs

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{25 Random Characters}.vbs = wscript.exe //B "%Application Data%\{25 Random characters}.vbs

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = explorer.exe, wscript.exe //B "%Application Data%\{25 Random Characters}.vbs

Other System Modifications

This Backdoor adds the following registry entries:

HKEY_CURRENT_USER\Software
ASPC = {25 Random Characters}

Backdoor Routine

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

  • http://{BLOCKED}.{BLOCKED}.12.175/gate.php?

Information Theft

This Backdoor gathers the following information on the affected computer:

  • HWID
  • Computer Name
  • User name
  • Product Name
  • OS Version
  • AV Products
  • Ram Size
  • CPU
  • GPU

Other Details

This Backdoor does the following:

  • Send information to its C&C server
  • Download file
  • Copy File
  • Update its dropped copies
  • Uninstall itself and its components
  • Elevates User privileges
  • It uses the following format to send the gathered information(Base 64 encoded):
    • {25 Random Characters}::OS version ::Computer Name::RAM size::AV Product::CPU::GPU

It adds the following scheduled tasks:

  • Task Name: ChromeUpdate
    • Trigger: ONLOGON
    • Action: "%Application Data%\{25 Random Characters}.vbs" /F

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 15.592.02
FIRST VSAPI PATTERN DATE: 31 Dec 2019
VSAPI OPR PATTERN File: 15.593.00
VSAPI OPR PATTERN Date: 01 Jan 2020

Step 1

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 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\Policies\Explorer\Run
    • {25 Random Characters}.vbs = wscript.exe //B "%Application Data%\{25 Random Characters}.vbs"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • {25 Random Characters}.vbs = wscript.exe //B "%Application Data%\{25 Random Characters}.vbs"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {25 Random Characters}.vbs = wscript.exe //B "%Application Data%\{25 Random Characters}.vbs"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Shell = wscript.exe //B "%Application Data%\{25 Random Characters}.vbs"
  • In HKEY_CURRENT_USER\Software
    • ASPC = {25 Random Characters}

Step 5

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.
  • %Common Startup%\{25 Random Characters}.vbs
  • %Application Data%\g_{25 Random Characters}.vbs_w.vbs
  • %Application Data%\{25 Random Characters}.vbs
  • %Application Data%\1192431963351_log.txt

Step 6

Deleting Scheduled Tasks

The following {Task Name} - {Task to be run} listed should be used in the steps identified below:

  • Task Name: ChromeUpdate
  • Task to be run: %Application Data%\{25 Random Characters}.vbs /F

For Windows 2000, Windows XP, and Windows Server 2003:

  1. Open the Windows Scheduled Tasks. Click Start>Programs>Accessories>
    System Tools>Scheduled Tasks.
  2. Locate each {Task Name} values listed above in the Name column.
  3. Right-click on the said file(s) with the aforementioned value.
  4. Click on Properties. In the Run field, check for the listed {Task to be run}.
  5. If the strings match the list above, delete the task.

For Windows Vista, Windows 7, Windows Server 2008, Windows 8, Windows 8.1, and Windows Server 2012:

  1. Open the Windows Task Scheduler. To do this:
    • On Windows Vista, Windows 7, and Windows Server 2008, click Start, type taskschd.msc in the Search input field, then press Enter.
    • On Windows 8, Windows 8.1, and Windows Server 2012, right-click on the lower left corner of the screen, click Run, type taskschd.msc, then press Enter.
  2. In the left panel, click Task Scheduler Library.
  3. In the upper-middle panel, locate each {Task Name} values listed above in the Name column.
  4. In the lower-middle panel, click the Actions tab. In the Details column, check for the {Task to be run} string.
  5. If the said string is found, delete the task.

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.VBS.YNOGA.A. 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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