Analysis by: Carlos Villegas Madrid
ALIASES:

Trojan-Ransom.Trigona (IKARUS)

 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: 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.

It drops files as ransom note.

  TECHNICAL DETAILS

File Size: 2,251,776 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 16 Mar 2023
Payload: Collects system information, Encrypts files, Modifies system registry

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:

  • 4E8F43A8-6586-803C2BEC → 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 Hash = {Malware Path}\{Malware File Name}.exe

Other System Modifications

This Ransomware adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Generated Hash = %User Temp%\how_to_decrypt.hta

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 does the following:

  • It loads its configuration found in its resource section named CFGS.
  • It checks for the presence of the following file that serves as its configuration file:
    • cfgs.txt
  • It encrypts the information it gathers and stores it on the authentication key, which is required during the negotiation procedure to retrieve files.
  • By default, It encrypts local drives and network drives.
  • It displays its ransom note after encryption.
  • For this specific sample, it contains code error that causes the ransom note to display as a blank .HTA file.

Ransomware Routine

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

  • how_to_decrypt.hta

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

  • Windows
  • System32

It appends the following extension to the file name of the encrypted files:

  • ._locked

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

  • {Encrypted Directory}\how_to_decrypt.hta
  • %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).)

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 18.452.02
FIRST VSAPI PATTERN DATE: 18 May 2023
VSAPI OPR PATTERN File: 18.453.00
VSAPI OPR PATTERN Date: 19 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:

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

Restart in Safe Mode

[ Learn More ]

Step 5

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 Hash = {Malware Path}\{Malware File Name}.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Generated Hash = %User Temp%\how_to_decrypt.hta

Step 6

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

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.Win32.TRIGONA.THCAFBC. 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.

Step 8

Restore encrypted files from backup.


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