Analysis by: Raymart Christian Yambot
ALIASES:

Win32:Dh-A [Heur] (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 drops files as ransom note.

  TECHNICAL DETAILS

File Size: 432,128 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 18 Jul 2023
Payload: Displays graphics/image, Displays message/message boxes, 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:

  • %Public%\bg.jpg

(Note: %Public% is the folder that serves as a repository of files or folders common to all users, which is usually C:\Users\Public in Windows Vista, 7, and 8.)

It adds the following processes:

  • cmd.exe /c for /F "tokens=*" %1 in ('wevtutil.exe el') DO wevtutil.exe cl "%1
  • cmd.exe /c start powershell.exe -WindowStyle Hidden -Command "Sleep -Milliseconds 1000; schtasks /delete /tn Rhsd /f;
  • cmd.exe /c vssadmin.exe Delete Shadows /All /Quiet
  • cmd.exe /c reg delete "HKCU\Contol Panel\Desktop" /v Wallpaper /f
  • cmd.exe /c reg delete "HKCU\Conttol Panel\Desktop" /v WallpaperStyle /f
  • cmd.exe /c reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\ActiveDesktop" /v NoChangingWallPaper /t REG_SZ /d 1 /f
  • cmd.exe /c reg add "HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\ActiveDesktop" /v NoChangingWallPaper /t REG_SZ /d 1 /f
  • cmd.exe /c reg add "HKCU\Control Panel\Desktop" /v Wallpaper /t REG_SZ /d "%Public%\bg.jpg" /f
  • cmd.exe /c reg add "HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\System" /v Wallpaper /t REG_SZ /d "%Public%\bg.jpg" /f
  • cmd.exe /c reg add "HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\System" /v WallpaperStyle /t REG_SZ /d 2 /f
  • cmd.exe /c reg add "HKCU\Control Panel\Desktop" /v WallpaperStyle /t REG_SZ /d 2 /f
  • rundll32.exe user32.dll,UpdatePerUserSystemParameters
  • cmd.exe /c start ping 127.0.0.1 -n 2

(Note: %Public% is the folder that serves as a repository of files or folders common to all users, which is usually C:\Users\Public in Windows Vista, 7, and 8.)

Other System Modifications

This Ransomware changes the desktop wallpaper by modifying the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
ActiveDesktop
NoChangingWallPaper = 1

(Note: The default value data of the said registry entry is 0.)

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Policies\
ActiveDesktop
NoChangingWallPaper = 1

(Note: The default value data of the said registry entry is 0.)

HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = %Public%\bg.jpg

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
Wallpaper = %Public%\bg.jpg

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
WallpaperStyle = 2

(Note: The default value data of the said registry entry is 0.)

HKEY_CURRENT_USER\Control Panel\Desktop
WallpaperStyle = 2

(Note: The default value data of the said registry entry is 0.)

It sets the system's desktop wallpaper to the following image:

  • %Public%\bg.jpg

Other Details

This Ransomware does the following:

  • It initializes resources based on the number of processors available in the system.
  • It encrypts all system drives from A to Z.

It accepts the following parameters:

  • -d {path to encrypt} → used to specify directory to encrypt
  • -sr
  • -nobg → used to disable modification of desktop wallpaper after encryption
  • -md5
  • -S → executes the following:
    • Avoids Ransomware Routine
    • Creates scheduled tasks named Rhsd

It adds the following scheduled tasks:

  • Task: Rhsd
  • Trigger: At system start Up
  • Action: "{Malware File Path}\{Malware File name}" -sr

Ransomware Routine

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

  • .bat
  • .bin
  • .cab
  • .cmd
  • .com
  • .cur
  • .diagcab
  • .diagcfg
  • .diagpkg
  • .drv
  • .dll
  • .exe
  • .hlp
  • .hta
  • .ico
  • .msi
  • .ocx
  • .ps1
  • .psm1
  • .scr
  • .sys
  • .ini
  • Thumbs.db
  • .url
  • .iso

It avoids encrypting files found in the following folders:

  • $Recycle.Bin
  • Boot
  • Documents and Settings
  • PerfLogs
  • ProgramData
  • Recovery
  • System Volume Information
  • Windows
  • $RECYCLE.BIN
  • ApzData

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

  • .rhysida

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

  • {Encrypted Directory}\CriticalBreachDetected.pdf

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 18.534.08
FIRST VSAPI PATTERN DATE: 27 Jun 2023
VSAPI OPR PATTERN File: 18.535.00
VSAPI OPR PATTERN Date: 28 Jun 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.XXPE50FFF070

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

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\ActiveDesktop
    • NoChangingWallPaper = 1
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\ActiveDesktop
    • NoChangingWallPaper = 1
  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • Wallpaper = %Public%\bg.jpg
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • Wallpaper = %Public%\bg.jpg
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • WallpaperStyle = 2
  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • WallpaperStyle = 2

Step 6

Deleting Scheduled Tasks while in Safe Mode

  1. Still in safe mode, the following {Task Name}-{Task to be run} listed should be used in the steps identified below:
    • Task Name: Rhsd
    • Task to be run: {Malware File Path}\{Malware File name} -sr
  2. For Windows 7 and Server 2008 (R2) users, click Start>Computer.
    • For Windows 8, 8.1, 10, and Server 2012 users, right-click on the lower left corner of the screen, then click File Explorer.
  3. In the Search Computer/This PC input box, type:
    • %System%\Tasks\{Task Name}
  4. Once located, select the file then press SHIFT+DELETE to delete it.
  5. Open Registry Editor. To do this:
    • For Windows 7 and Server 2008 (R2) users, click the Start button, type regedit in the Search input field, and press Enter.
    • For Windows 8, 8.1, 10, and Server 2012 (R2) users, right-click on the lower left corner of the screen, click Run, type regedit in the text box
  6. In the left panel of the Registry Editor window, double-click the following:
    • HKEY_LOCAL_MACHINE>SOFTWARE>Microsoft>Windows NT>CurrentVersion>Schedule>TaskCache>Tree>{Task Name}
  7. Locate the created entry and take note of the registry value's data:
    • ID={Task Data}
  8. After taking note of the data, delete the registry key:
    • HKEY_LOCAL_MACHINE>SOFTWARE>Microsoft>Windows NT>CurrentVersion>Schedule>TaskCache>Tree>{Task Name}
  9. In the left panel of the Registry Editor window, double-click the following:
    • HKEY_LOCAL_MACHINE>SOFTWARE>Microsoft>Windows NT>CurrentVersion>Schedule>TaskCache>Tasks
  10. Still in the left panel, locate and delete the registry key with the same name as the located Task Data in step #6:
    • ={Task Data}
  11. Close Registry Editor.

Step 7

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.
  • %Public%\bg.jpg
  • {Encrypted Directory}\CriticalBreachDetected.pdf

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.Win64.RHYSIDA.SM. 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 9

Restore encrypted files from backup.

Step 10

Reset your Desktop properties

[ Learn More ]


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