Analysis by: Leidryn Saludez
ALIASES:

UDS:Trojan-Ransom.Win32.Agent.gen (KASPERSKY)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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

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.

It drops files as ransom note.

  TECHNICAL DETAILS

File Size: 1,143,808 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 10 Feb 2023
Payload: Collects system information, Modifies system registry, Encrypts files

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 adds the following processes:

  • "%System%\mshta.exe" "%User Temp%\how_to_decrypt.hta"

(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 mutexes to ensure that only one of its copies runs at any one time:

  • 4E8F43A8-15C1-803C2BEC → derived from computer name

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{Generated ID 1} = {malware file path}\{malware name}.exe

Information Theft

This Ransomware gathers the following data:

  • OS Version
  • Available disk drives
  • Free disk space on all available drives
  • Keyboard Layout
  • System Locale
  • Username
  • Computer Name
  • Network Configuration Information

Other Details

This Ransomware adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{Generated ID 2} = %User Temp%\how_to_decrypt.hta

It does the following:

  • By default, It encrypts local drives and network drives.
  • It displays its ransom note after encryption.

It accepts the following parameters:

  • /r → Allows the encryption of files in a random order
  • /full → Encrypt the whole content of the target file (if not used, only the first 0x80000 bytes/512kb are encrypted)
  • /erase → Deletes the content of the target files.
  • /!autorun → Does not create the autorun registry entry.
  • /is_testing → For testing purposes, used with /test_cid and /test_vid
  • /test_cid → Uses the specified Computer ID instead of generating one
  • /test_vid → Uses the specified Victim ID instead of the one in the configurations
  • /p → Specifies the path to encrypt
  • /path → Specifies the path to encrypt
  • /!local → Avoids encrypting local files
  • /!lan → Avoids encrypting network shares
  • /shdwn →Forces shutdown of the machine after encryption
  • /autorun_only → Create Autorun registry entry

Ransomware Routine

This Ransomware avoids encrypting files with the following strings in their file name:

  • how_to_decrypt.hta
  • how_to_decrypt.txt

It avoids encrypting files with the following strings in their file path:

  • Windows
  • System32

It renames encrypted files using the following names:

  • available_for_trial.{random}.{random}._locked
  • {random}.{random}._locked

It drops the following file(s) as ransom note:

  • %User Temp%\how_to_decrypt.hta
  • {Encrypted Directory}\how_to_decrypt.hta
  • {Drive Letter}\how_to_decrypt.hta

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 18.424.08
FIRST VSAPI PATTERN DATE: 04 May 2023
VSAPI OPR PATTERN File: 18.425.00
VSAPI OPR PATTERN Date: 05 May 2023

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.XXPE50FFF069

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
    • {Generated ID 1} = {malware file path}\{malware name}.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {Generated ID 2} = %User Temp%\how_to_decrypt.hta

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.
  • %User Temp%\how_to_decrypt.hta
  • {Encrypted Directory}\how_to_decrypt.hta
  • {Drive Letter}\how_to_decrypt.hta

Step 6

Scan your computer with your Trend Micro product to delete files detected as Ransom.Win32.TRIGONA.YMDBJ. 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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