Analysis by: Khristian Joseph Morales

ALIASES:

W32/MAUICRYPT.YACC5!tr.ransom (FORTINET)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

This Ransomware 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: 781,998 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 31 Mar 2022
Payload: Drops files, Adds processes

Arrival Details

This Ransomware 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 Ransomware drops the following files:

  • {Malware Path}\maui.evd → RSA private key generated at runtime
  • {Malware Path}\maui.key → RSA public key generated at runtime
  • {Malware Path}\maui.log → Log file containing output console output from execution
  • %User Temp%\dgod.bat → Used to delete itself

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

It adds the following processes:

  • %System%\cmd.exe /c start /b "" cmd /c "%User Temp%\dgod.bat"
  • ping localhost -n 1
  • del /f /q "{Malware Path}\{Malware Filename}"
  • TASKKILL /IM "{Malware Path}\{Malware Filename}"

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

Other Details

This Ransomware does the following:

  • It does not rename encrypted files.
  • It does not drop a ransom note.
  • It requires to be executed with an argument {target path} to proceed to encryption.

It accepts the following parameters:

  • -p {Path} → Set log directory
  • -t {n} → Set thread count
  • -x → Delete itself
  • {target path} → Encrypts only specified path

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 17.476.07
FIRST VSAPI PATTERN DATE: 31 Mar 2022
VSAPI OPR PATTERN File: 17.477.00
VSAPI OPR PATTERN Date: 01 Apr 2022

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.XXPE50FFF058

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

Identify and terminate files detected as Ransom.Win32.MAUICRYPT.YACC5

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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.  
  • {Malware Path}\maui.evd
  • {Malware Path}\maui.key
  • {Malware Path}\maui.log
  • %User Temp%\dgod.bat

Step 6

Scan your computer with your Trend Micro product to delete files detected as Ransom.Win32.MAUICRYPT.YACC5. 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:

Step 7

Restore encrypted files from backup.


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