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Ransom.MSIL.TENCRYPT.THCAABD

March 29, 2024
 Analysis by: John Rainier Navato
 ALIASES:

Ransom:MSIL/Filecoder.PK!MSR (MICROSOFT)

 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 drops files as ransom note. It avoids encrypting files with the following file extensions.

  TECHNICAL DETAILS

File Size:

22,528 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

11 Mar 2024

Payload:

Drops files, Terminates processes, Modifies system registry, Displays graphics/image, 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%\cmd.exe /C vssadmin delete shadows /all /quiet & wmic shadowcopy delete
  • %System%\cmd.exe /C bcdedit /set {default} bootstatuspolicy ignoreallfailures & bcdedit /set {default} recoveryenabled no
  • %System%\cmd.exe /C wbadmin delete catalog -quiet

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

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
RESTORE_FILES-{Computer Name} = {Malware File Path}\{Malware File Name}.{Malware File Extension}

Other System Modifications

This Ransomware sets the system's desktop wallpaper to the following image:

  • %User Temp%\{9 Random Characters}.jpg

Process Termination

This Ransomware terminates the following processes if found running in the affected system's memory:

  • agntsvc
  • CNTAoSMgr
  • code
  • dbeng50
  • dbsnmp
  • encsvc
  • excel
  • firefoxconfig
  • infopath
  • isqlplussvc
  • mbamtray
  • msaccess
  • msftesql
  • mspub
  • mydesktopqos
  • mydesktopservice
  • mysqld
  • mysqld-nt
  • mysqld-opt
  • Ntrtscan
  • ocautoupds
  • ocomm
  • ocssd
  • onenote
  • oracle
  • outlook
  • PccNTMon
  • powerpnt
  • ProcessHacker
  • sqbcoreservice
  • sqlagent
  • sqlbrowser
  • sqlservr
  • sqlwriter
  • steam
  • synctime
  • tbirdconfig
  • thebat
  • thebat64
  • thunderbird
  • tmlisten
  • VBoxSVC
  • VirtualBoxVM
  • visio
  • vmplayer
  • winword
  • wordpad
  • wps
  • xfssvccon
  • zoolz

Other Details

This Ransomware does the following:

  • It checks if the size of the file to encypt is less than or greater than 524,288 bytes
    • If it is less than 524,288 bytes, it will encrypt the whole file.
    • If it is greater than 524,288 bytes, it will use intermittent encryption - First 131,072 bytes, another 131,072 bytes from the middle of the file, and the last 131,072 bytes
  • It empties the recycle bin.
  • It encrypts its targeted files twice.
  • It avoids encrypting files with the following file names:
    • autorun.inf
    • boot.ini
    • bootfont.bin
    • bootmgfw.efi
    • bootmgr
    • bootmgr.efi
    • desktop.ini
    • iconcache.db
    • ntuser.dat
    • ntuser.ini
    • RESTORE_FILES-{Computer Name}.txt
    • thumbs.db

Ransomware Routine

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

  • c:\perflogs
  • c:\program files
  • c:\program files (x86)
  • c:\programdata
  • c:\users\all users
  • c:\users\default
  • c:\windows
  • c:\windows.old

It avoids encrypting files found in the following folders:

  • $recycle.bin
  • $windows.~bt
  • $windows.~ws
  • appdata
  • documents and settings
  • intel
  • mozilla
  • PerfLogs
  • perflogs
  • program files
  • program files (x86)
  • programdata
  • system volume information
  • windows
  • windows.old
  • windows.old.old

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

  • .crypted

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

  • {Encrypted File Path}\RESTORE_FILES-{Computer Name}.txt

It avoids encrypting files with the following file extensions:

  • {Files with no file extension}
  • .386
  • .adv
  • .ani
  • .bat
  • .bin
  • .cab
  • .cmd
  • .com
  • .cpl
  • .crypted
  • .cur
  • .deskthemepack
  • .diagcab
  • .diagcfg
  • .diagpkg
  • .dll
  • .drv
  • .exe
  • .hlp
  • .hta
  • .icl
  • .icns
  • .ico
  • .ics
  • .idx
  • .key
  • .ldf
  • .lnk
  • .lock
  • .mod
  • .mpa
  • .msc
  • .msi
  • .msp
  • .msstyles
  • .msu
  • .nls
  • .nomedia
  • .ocx
  • .pdb
  • .prf
  • .ps1
  • .rom
  • .rtp
  • .scr
  • .shs
  • .spl
  • .sys
  • .theme
  • .themepack
  • .wpx

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

19.210.04

FIRST VSAPI PATTERN DATE:

11 Mar 2024

VSAPI OPR PATTERN File:

19.211.00

VSAPI OPR PATTERN Date:

12 Mar 2024

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.XXPE50FFF077

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
    • RESTORE_FILES-{Computer Name} = {Malware File Path}\{Malware File Name}.{Malware File Extension}

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 File Path}\RESTORE_FILES-{Computer Name}.txt
  • %User Temp%\{9 Random Characters}.jpg

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.MSIL.TENCRYPT.THCAABD. 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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