Analysis by: Christopher Daniel So
 PLATFORM:

Windows

 OVERALL RISK RATING:
 REPORTED INFECTION:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Backdoor may be dropped by other malware.

  TECHNICAL DETAILS

File Size: 8,725 bytes
File Type: PS1, VBS
Memory Resident: Yes
Initial Samples Received Date: 09 Nov 2017

Arrival Details

This Backdoor may be dropped by the following malware:

  • X2KM_TOXOCARA.A

Installation

This Backdoor drops the following component file(s):

  • %System Root%:\Users\Public\Libraries\id.txt
  • %System Root%:\Users\Public\Libraries\{random number}.vbs
  • %System Root%:\Users\Public\Libraries\{random number 1}.txt
  • %System Root%:\Users\Public\Libraries\{random number 2}.txt

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

It creates the following folders:

  • %System Root%:\Users\Public\Libraries
  • %System Root%:\Users\Public\Libraries\dn
  • %System Root%:\Users\Public\Libraries\up
  • %System Root%:\Users\Public\Libraries\tp

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

Other System Modifications

This Backdoor deletes the following files:

  • %System Root%:\Users\Public\test5.vbs (assumed file name of the component dropped by X2KM_TOXOCARA.A)
  • %System Root%:\Users\Public\test5.txt (assumed file name of itself dropped by X2KM_TOXOCARA.A)

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

Download Routine

This Backdoor accesses the following websites to download files:

  • http://{BLOCKED}lys.com/index.aspx?id=_2

It saves the files it downloads using the following names:

  • %System Root%:\Users\Public\Libraries\dn\{random file name}

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

NOTES:

Other Details

It creates a Scheduled Task named GoogleUpdateTasksMachineUI that executes %System Root%:\Users\Public\Libraries\{random number}.vbs every 3 minutes. The VBS file in turn executes the following component files using PowerShell:

  • %System Root%:\Users\Public\Libraries\{random number 1}.txt
  • %System Root%:\Users\Public\Libraries\{random number 1}.txt

It encrypts and uploads all files in the folder %System Root%:\Users\Public\Libraries\up to the following URL using HTTP POST.

  • http://{BLOCKED}lys.com/index.aspx?id=_3

Backdoor Routine

It connects to the following URL to download an executable file:

  • http://{BLOCKED}lys.com/index.aspx?id=_1

It saves the file it downloads using the following name:

  • %System Root%:\Users\Public\Libraries\dn\{random filename}

It executes the downloaded executable file using CMD.EXE, and redirects the output of the executable file to %System Root%:\Users\Public\Libraries\dn\{random filename}.txt. It then encrypts and uploads %System Root%:\Users\Public\Libraries\dn\{random filename}.txt to the following URL using HTTP POST:

  • http://{BLOCKED}lys.com/index.aspx?id=_3

It then deletes the downloaded file %System Root%:\Users\Public\Libraries\dn\{random filename}.

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 13.770.07
FIRST VSAPI PATTERN DATE: 10 Nov 2017
VSAPI OPR PATTERN File: 13.771.00
VSAPI OPR PATTERN Date: 10 Nov 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

Remove the malware/grayware file that dropped/downloaded BKDR_TOXOCARA.A. (Note: Please skip this step if the threat(s) listed below have already been removed.)

Step 3

Terminate a malware/grayware process

[ Learn More ]

*Note: If the detected process is not displayed in theWindows Task Manager, continue doing the next steps.

    • powershell.exe

Step 4

To delete the added Scheduled Task:

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

  1. Click on Start>Programs>Accessories>System Tools>Scheduled Tasks
  2. Double-click on a job file.
  3. Check if the malware path and file name is in the Run: box.
  4. If it does, delete the job file.
  5. Repeat step 2-4 for the remaining job files.

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, select a Task.
  4. Check if the selected task starts the malware automatically. To do this, check the value in the Details column under the Actions tab in the lower-middle panel.
  5. If the malware path and file name is found, press DELETE and click Yes to delete the task.
  6. Repeat steps 3-5 for the remaining tasks.

Step 5

Search and delete this folder

[ 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.
  • %System Root%:\Users\Public\Libraries

Step 6

Scan your computer with your Trend Micro product to delete files detected as BKDR_TOXOCARA.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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