Ransom.Win32.STOP.AN

 Analysis by: Henry Alarcon Jr.

 ALIASES:

Win32.Trojan-Ransom.STOP.VZ9O0W (GData), Trojan:Win32/Skeeyah.A!MTB, (Microsoft), W32/Kryptik.GVDM!tr (Fortinet)

 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. As of this writing, the said sites are inaccessible.

It drops files as ransom note.

  TECHNICAL DETAILS

File Size:

414,208 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

02 Aug 2019

Payload:

Connects to URLs/IPs, Downloads files, Displays message/message boxes, Modifies system registry

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 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:

  • icacls "%AppDataLocal%\{GUID}" /deny *S-1-1-0:(OI)(CI)(DE,DC)
  • "{Executed Malware File Path}\{Executed Malware File Name}.exe" --Admin- IsNotAutoStart IsNotTask ← malware is executed as Admin and not executed as autorun registry or via task

(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} ← created two(2) folders, one(1) for drop copy and one(1) for downloaded files.

(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 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/files/cost/updatewin.exe
  • http://{BLOCKED}ug/files/cost/updatewin1.exe
  • http://{BLOCKED}ug/files/cost/updatewin2.exe
  • http://{BLOCKED}ug/files/cost/3.exe
  • http://{BLOCKED}ug/files/cost/4.exe
  • http://{BLOCKED}ug/files/cost/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 the "--Service" and "--ForNetRes" to perform it's routine:
    • http://{BLOCKED}ug/vbcbcvbcbv51/dgdgdfgd/get.php?pid={Hash PID}&first={true|false}
  • 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%\{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
  • It connects to the following URL(s) to get the affected system's IP address and location:
    • https://{BLOCKED}i.{BLOCKED}p.ua/geo.json
      • It terminate and delete itself on the affected sysyem if the return of the IP address location are 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:

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

It avoids encrypting files found in the following folders:

  • C:\Users\Public\
  • C:\SystemID\
  • C:\Users\Default User\
  • C:\Users\Public\
  • C:\Users\All Users\
  • C:\Users\Default\
  • C:\Documents and Settings\
  • C:\ProgramData\
  • C:\Recovery\
  • C:\System Volume Information\
  • C:\Users\%username%\AppData\Roaming\
  • C:\Users\%username%\AppData\Local\
  • C:\Windows\
  • C:\PerfLogs\
  • C:\ProgramData\Microsoft\
  • C:\ProgramData\Package Cache\
  • C:\Users\Public\
  • C:\$Recycle.Bin\
  • C:\$WINDOWS.~BT\
  • C:\dell\
  • C:\Intel\
  • C:\MSOCache\
  • C:\Program Files\
  • C:\Program Files (x86)\
  • C:\Games\
  • C:\Windows.old\
  • D:\Users\%username%\AppData\Roaming\
  • D:\Users\%username%\AppData\Local\
  • D:\Windows\
  • D:\PerfLogs\
  • D:\ProgramData\Desktop\
  • D:\ProgramData\Microsoft\
  • D:\ProgramData\Package Cache\
  • D:\Users\Public\
  • D:\$Recycle.Bin\
  • D:\$WINDOWS.~BT\
  • D:\dell\
  • D:\Intel\
  • D:\MSOCache\
  • D:\Program Files\
  • D:\Program Files (x86)\
  • D:\Games\
  • E:\Users\%username%\AppData\Roaming\
  • E:\Users\%username%\AppData\Local\
  • E:\Windows\
  • E:\PerfLogs\
  • E:\ProgramData\Desktop\
  • E:\ProgramData\Microsoft\
  • E:\ProgramData\Package Cache\
  • E:\Users\Public\
  • E:\$Recycle.Bin\
  • E:\$WINDOWS.~BT\
  • E:\dell\
  • E:\Intel\
  • E:\MSOCache\
  • E:\Program Files\
  • E:\Program Files (x86)\
  • E:\Games\
  • F:\Users\%username%\AppData\Roaming\
  • F:\Users\%username%\AppData\Local\
  • F:\Windows\
  • F:\PerfLogs\
  • F:\ProgramData\Desktop\
  • F:\ProgramData\Microsoft\
  • F:\Users\Public\
  • F:\$Recycle.Bin\
  • F:\$WINDOWS.~BT\
  • F:\dell\
  • F:\Intel\

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

  • .cosakos

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

  • {Encrypted File Directory}\_readme.txt

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

15.272.05

FIRST VSAPI PATTERN DATE:

02 Aug 2019

VSAPI OPR PATTERN File:

15.273.00

VSAPI OPR PATTERN Date:

03 Aug 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.AN

[ 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%\{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%\{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%\{GUID} ← for drop copy
  • %AppDataLocal%\{GUID} ← for downloaded files

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

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

Step 9

Restore encrypted files from backup.


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