Analysis by: Henry Alarcon Jr.
ALIASES:

Trojan-Ransom.Win32.Stop.ba (Kaspersky), Trojan:Win32/Kryptik.BN!MTB (Microsoft),Trojan[Ransom]/Win32.STOP (Antiy-AVL)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: Yes

  • 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 saves downloaded files into the said created folder.

It drops files as ransom note.

  TECHNICAL DETAILS

File Size: 578,048 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 01 Jul 2019
Payload: Connects to URLs/IPs, Downloads files, Displays message/message boxes

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%\{Hash of Machine GUID}\{malware file name}.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:

  • "{Executed Malware File Path}\{Executed Malware File Name}.exe" --Task -> malware is executed via Task Scheduler
  • icacls "%AppDataLocal%\{Hash of Machine GUID}" /deny *S-1-1-0:(OI)(CI)(DE,DC)
  • "%AppDataLocal%\{Hash of Machine GUID}\updatewin.exe -- Admin" ← downloaded and detected as Trojan.Win32.MALREP.THOABAAI
  • "%AppDataLocal%\{Hash of Machine GUID}\updatewin1.exe -- Admin" ← downloaded and detected as Trojan.Win32.MALREP.THOABAAI

(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:

  • %AppDataLocal%\{Hash of Machine GUID}

(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 adds the following mutexes to ensure that only one of its copies runs at any one time:

  • {Hash of Machine GUID}

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%\{Hash of Machine GUID}\{Malware File Name}.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}.ug/tesptc/penelop/updatewin.exe
  • http://{BLOCKED}.ug/tesptc/penelop/updatewin1.exe
  • http://{BLOCKED}.ug/tesptc/penelop/updatewin2.exe
  • As of this writing, below the following sites are inaccessible:
    • http://{BLOCKED}.ug/tesptc/penelop/3.exe
    • http://{BLOCKED}.ug/tesptc/penelop/4.exe
    • http://{BLOCKED}.ug/tesptc/penelop/5.exe

Trend Micro detects the dowloaded file as:

  • Trojan.Win32.MALREP.THOABAAI

It saves downloaded files into the said created folder.

Other Details

This Ransomware connects to the following URL(s) to get the affected system's IP address:

  • https://api.2ip.ua/geo.json

It does the following:

  • Connects to the URL to get the arguments needed for the "--Service" and "--ForNetRes" to perform it's routine:
    • http://{BLOCKED}.ug/AJshdd74568oHIUHSusf6441/Asjdioaiuf738/get.php?pid={HASH PID}
  • Checks if there is an existing copy of itself in %AppDataLocal% then delete it and drops a copy of itself at %AppDataLocal%
  • Adds the following Scheduled Task:
    • Task Name: Time Trigger Task
      Schedule: Once, after triggered repeat every 5 mins. Trigger expires at 5/2/2030 8:00 AM
      Task to be run: "%AppDataLocal%\{Hash of Machine GUID}\{Malware File Name}.exe"
  • It accepts/ add the following arguments to check its execution:
    • --Admin -> run the malware as admin
    • --AutoStart -> executes using autorun registry keys.
    • --ForNetRes {Argumet from the URL} {Argument From the URL}
    • --Service {PID of the Parent Malware Running} {Argumet from the URL} {Argument From the URL}
    • IsAutoStart -> Execute malware as an autostart
    • IsNotAutoStart -> Execute malware not as an autostart
    • IsTask/Task -> Execute malware as a task
    • IsNotTask -> Execute malware not as a task

Ransomware Routine

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

  • .sys
  • .bat
  • .dll
  • .lnk
  • .ini
  • _readme.txt
  • ntuser.dat

It avoids encrypting files found in the following folders:

  • C:\$Recycle.Bin\
  • C:\PerfLogs\
  • C:\$WINDOWS.~BT\
  • C:\dell\
  • C:\Intel\
  • C:\MSOCache\
  • C:\Games\
  • C:\Windows.old\
  • %AppDataLocal%
  • %Application Data%
  • %Windows%
  • %ProgramData%\Microsoft\
  • %ProgramData%\Package Cache\
  • %ProgramData%\Desktop\
  • %Public%
  • %Program Files% ; (for both 32 and 64 bit OS)
  • {Logical Drive Letter}\Users\%username%\AppData\Roaming\
  • {Logical Drive Letter}\Users\%username%\AppData\Local\
  • {Logical Drive Letter}\Windows\
  • {Logical Drive Letter}\PerfLogs\
  • {Logical Drive Letter}\ProgramData\Desktop\
  • {Logical Drive Letter}\ProgramData\Microsoft\
  • {Logical Drive Letter}\ProgramData\Package Cache\
  • {Logical Drive Letter}\Users\Public\
  • {Logical Drive Letter}\$Recycle.Bin\
  • {Logical Drive Letter}\$WINDOWS.~BT\
  • {Logical Drive Letter}\dell\
  • {Logical Drive Letter}\Intel\
  • {Logical Drive Letter}\MSOCache\
  • {Logical Drive Letter}\Program Files\
  • {Logical Drive Letter}\Program Files (x86)\
  • {Logical Drive Letter}\Games\

(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).. %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.. %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This contains application data for all users. This is usually C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.. %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.. %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000(32-bit), Server 2003(32-bit), XP, Vista(64-bit), 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit) , or C:\Program Files (x86) in Windows XP(64-bit), Vista(64-bit), 7(64-bit), 8(64-bit), 8.1(64-bit), 2008(64-bit), 2012(64-bit) and 10(64-bit).)

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

  • .litar

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

  • {Encrypted File Directory}\_readme.txt

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 15.208.04
FIRST VSAPI PATTERN DATE: 01 Jul 2019
VSAPI OPR PATTERN File: 15.209.00
VSAPI OPR PATTERN Date: 02 Jul 2019

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

Identify and terminate files detected as Ransom.Win32.STOP.THGOAAI

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 4

Deleting Scheduled Tasks

The following {Task Name} - {Task to be run} listed should be used in the steps identified below:

  • Task Name: Time Trigger Task
  • Task to be run: "%AppDataLocal%\{Hash of Machine GUID}\{Malware File Name}.exe"

For Windows 2000, Windows XP, and Windows Server 2003:

  1. Open the Windows Scheduled Tasks. Click Start>Programs>Accessories>
    System Tools>Scheduled Tasks.
  2. Locate each {Task Name} values listed above in the Name column.
  3. Right-click on the said file(s) with the aforementioned value.
  4. Click on Properties. In the Run field, check for the listed {Task to be run}.
  5. If the strings match the list above, delete the task.

For Windows Vista, Windows 7, Windows Server 2008, Windows 8, Windows 8.1, and Windows Server 2012:

  1. Open the Windows Task Scheduler. To do this:
    • On Windows Vista, Windows 7, and Windows Server 2008, click Start, type taskschd.msc in the Search input field, then press Enter.
    • On Windows 8, Windows 8.1, and Windows Server 2012, right-click on the lower left corner of the screen, click Run, type taskschd.msc, then press Enter.
  2. In the left panel, click Task Scheduler Library.
  3. In the upper-middle panel, locate each {Task Name} values listed above in the Name column.
  4. In the lower-middle panel, click the Actions tab. In the Details column, check for the {Task to be run} string.
  5. If the said string is found, delete the task.

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
    • SysHelper = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • SysHelper = "%AppDataLocal%\{Hash of Machine GUID}\{Malware File Name}.exe --AutoStart"

Step 6

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %AppDataLocal%\{Hash of Machine GUID}

Step 7

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 Directory}\_readme.txt
  • %System Root%\SystemID\PersonalID.txt

Step 8

Restore encrypted files from backup.

Step 9

Scan your computer with your Trend Micro product to delete files detected as Ransom.Win32.STOP.THGOAAI. 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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