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Ransom.MSIL.VYSMALL.THCOEBD

April 18, 2024
 Analysis by: Leidryn Saludez
 ALIASES:

Win32:Malware-gen (AVAST)

 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.

It encrypts files found in specific folders.

  TECHNICAL DETAILS

File Size:

7,168 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

04 Mar 2024

Payload:

Drops files, 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 drops the following files:

  • {Encrypted Directory}\README{1-10}.txt → a text file that contains only "KYKY" in it.

Other Details

This Ransomware encrypts files with the following extensions:

  • .txt
  • .docx
  • .pdf

It does the following:

  • It opens CMD to display the following that serves as the ransom note
    • File Encrypted: {Original file name of the encrypted file}
    • Ransomware Note: Your files have been encrypted. Contact us to get the decryption key.
    • Public Key: {public key of each file}
    • Created README file: {Encrypted Directory}\README{1-10}.txt

Ransomware Routine

This Ransomware encrypts files found in the following folders:

  • %Desktop%
  • %User Profile%\Links
  • %User Profile%\Contacts
  • %User Profile%\Documents
  • %User Profile%\Downloads
  • %User Profile%\Pictures
  • %User Profile%\Music
  • %User Profile%\OneDrive
  • %User Profile%\Saved Games
  • %User Profile%\Favorites
  • %User Profile%\Searches
  • %User Profile%\Videos

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

It renames encrypted files using the following names:

  • {8 Random Characters}.e4aibjtrguqlyaow

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

19.198.04

FIRST VSAPI PATTERN DATE:

05 Mar 2024

VSAPI OPR PATTERN File:

19.199.00

VSAPI OPR PATTERN Date:

06 Mar 2024

Step 1

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 2

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 3

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.  
  • {Encrypted Directory}\README{1-10}.txt

Step 4

Restore encrypted files from backup.

Step 5

Scan your computer with your Trend Micro product to delete files detected as Ransom.MSIL.VYSMALL.THCOEBD. 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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