Ransom.Win32.STOP.THHOAAI

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 saves downloaded files into the said created folder. As of this writing, the said sites are inaccessible.

It drops files as ransom note.

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 copies of itself into the affected system:

• %AppDataLocal%\{GUID}\{malware filename}.exe

(Note: %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It drops the following files:

• %System Root%\SystemID\PersonalID.txt

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

It adds the following processes:

• icacls "%AppDataLocal%\{GUID}" /deny *S-1-1-0:(OI)(CI)(DE,DC)

(Note: %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It creates the following folders:

• %System Root%\SystemID
• %AppDataLocal%\{GUID} - two folders created for dropped copy and downloaded files, respectively.

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local 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:

• {FBB4BCC6-05C7-4ADD-B67B-A98A697323C1}
• {1D6FC66E-D1F3-422C-8A53-C0BBCF3D900D}

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
SysHelper = ""%AppDataLocal%\{GUID}\{malware filename}.exe" --AutoStart"

Other System Modifications

This Ransomware adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion
SysHelper = 1

Download Routine

This Ransomware connects to the following website(s) to download and execute a malicious file:

• http://{BLOCKED}2.{BLOCKED}g/tesptc/penelop/updatewin.exe
• http://{BLOCKED}2.{BLOCKED}g/tesptc/penelop/updatewin1.exe
• http://{BLOCKED}2.{BLOCKED}g/tesptc/penelop/updatewin2.exe
• http://{BLOCKED}2.{BLOCKED}g/tesptc/penelop/3.exe
• http://{BLOCKED}2.{BLOCKED}g/tesptc/penelop/4.exe
• http://{BLOCKED}2.{BLOCKED}g/tesptc/penelop/5.exe

It saves downloaded files into the said created folder.

As of this writing, the said sites are inaccessible.

Other Details

This Ransomware does the following:

• Connects to the URL to get the arguments needed for "--Service" and "--ForNetRes" to perform its routine:
  
  • http://bruze2.ug/AJsh436ot83huidfgdfg24/asd7643it3hjkdfg/get.php?pid={PID hash}&first={true|false}
• Adds the following Scheduled Task:
  
  • Task Name: Time Trigger Task
  Trigger: Every 5 minutes
  Task to be run: "%AppDataLocal%\{GUID}\{malware filename}.exe"
• It accepts or adds the following arguments to check its execution:
  
  • --Admin -> runs the malware as admin
  • --AutoStart -> executes using autorun registry keys.
  • --ForNetRes {argument/s from URL}
  • --Service {process ID of parent malware} {argument/s from URL}
  • IsAutoStart/IsNotAutoStart -> executes malware as an autostart or not
  • IsTask/IsNotTask -> executes malware as a task or not
• It connects to the following URL(s) to get the affected system's IP address and location:
  • https://api.{BLOCKED}p.ua/geo.json
    • It terminates and deletes itself on the affected system if the return of the IP address location is any of the following:
      • RU (Russia)
      • BY (Belarus)
      • UA (Ukraine)
      • AZ (Azerbaijan)
      • AM (Armenia)
      • TJ (Tajikistan)
      • KZ (Kazakhstan)
      • KG (Kyrgyzstan)
      • UZ (Uzbekistan)
      • SY (Syrian Arab Republic)

Ransomware Routine

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

• .bat
• .blf
• .DLL
• .dll
• .ini
• .lnk
• .regtrans-ms
• .sys
• ntuser.dat
• ntuser.dat.LOG1
• ntuser.dat.LOG2
• ntuser.pol

It avoids encrypting files found in the following folders:

• {drive letter}\Windows
• {drive letter}\Windows.old
• {drive letter}\$Recycle.Bin
• {drive letter}\$WINDOWS.~BT
• {drive letter}\dell
• {drive letter}\Documents and Settings
• {drive letter}\Games
• {drive letter}\Intel
• {drive letter}\MSOCache
• {drive letter}\PerfLogs
• {drive letter}\Program Files (x86)
• {drive letter}\Program Files (x86)\Google
• {drive letter}\Program Files (x86)\Internet Explorer
• {drive letter}\Program Files (x86)\Mozilla Firefox
• {drive letter}\Program Files\
• {drive letter}\Program Files\Google
• {drive letter}\Program Files\Internet Explorer
• {drive letter}\Program Files\Mozilla Firefox
• {drive letter}\ProgramData
• {drive letter}\ProgramData\Desktop
• {drive letter}\ProgramData\Microsoft
• {drive letter}\ProgramData\Package Cache
• {drive letter}\Recovery
• {drive letter}\System Volume Information
• {drive letter}\SystemID
• {drive letter}\Users\%username%\AppData\Local
• {drive letter}\Users\%username%\AppData\Roaming
• {drive letter}\Users\All Users
• {drive letter}\Users\Default User
• {drive letter}\Users\Default
• {drive letter}\Users\Public

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

• .todar

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

• {folder of encrypted files}\_readme.txt