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Trojan.Win64.COMBACKER.YABA-A

January 26, 2021
 Analysis by: Joshua Paul Ignacio
 ALIASES:

Trojan.Win64.Agent (IKARUS), Trojan:Win64/Comebacker.A!dha (MICROSOFT)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware


This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size:

464,384 bytes

File Type:

DLL

Memory Resident:

No

Initial Samples Received Date:

26 Jan 2021

Payload:

Modifies system registry

Arrival Details

This Trojan 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 Trojan drops the following files:

It adds the following processes:

  • %System%\rundll32.exe %All Users Profile%\VMware\vmnat-update.bin,OCSP_resp_find lxUi5CZ0IV45j89Y 4901

(Note: %All Users Profile% is the common user's profile folder, which is usually C:\Documents and Settings\All Users on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit). )

It creates the following folders:

  • %All Users Profile%\VMware

(Note: %All Users Profile% is the common user's profile folder, which is usually C:\Documents and Settings\All Users on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit). )

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
OneDrive Update = %System%\rundll32.exe %All Users Profile%\VMware\vmnat-update.bin,OCSP_resp_find lxUi5CZ0IV45j89Y 4901

Other Details

This Trojan does the following:

  • If the following processes are found running on the machine it will not create the registry entry above:
    • avp.exe
    • avastui.exe

It accepts the following parameters:

  • Bx9yb37GEcJNK6bt 4901 → to proceed with its routine

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

16.502.03

FIRST VSAPI PATTERN DATE:

27 Jan 2021

VSAPI OPR PATTERN File:

16.503.00

VSAPI OPR PATTERN Date:

28 Jan 2021

Step 1

Trend Micro Predictive Machine Learning detects and blocks malware at the first sign of its existence, before it executes on your system. When enabled, your Trend Micro product detects this malware under the following machine learning name:

    • Troj.Win32.TRX.XXPE50FFF040

Step 2

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 3

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 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
    • OneDrive Update = %System%\rundll32.exe C:\ProgramData\VMware\vmnat-update.bin,OCSP_resp_find lxUi5CZ0IV45j89Y 4901

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.
  • %All Users Profile%\VMWare\vmnat-update.bin

Step 6

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.
  • %All Users Profile%\VMWare

Step 7

Scan your computer with your Trend Micro product to delete files detected as Trojan.Win64.COMBACKER.YABA-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 the following Trend Micro Support pages for more information:


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