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Ransom.Win32.STOP.THCAAAI

March 14, 2019
 Analysis by: Noel Anthony Llimos
 ALIASES:

Trojan.Win32.Scar.rtsm (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

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:

336,896 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

11 Mar 2019

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}\{Executed 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, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista, 7, and 8.)

It adds the following processes:

  • icacls "%AppDataLocal%\{Hash of Machine GUID}" /deny *S-1-1-0:(OI)(CI)(DE,DC)
  • %AppDataLocal%\{Hash of Machine GUID}\{Executed Malware Filename}.exe --Task
  • "{Executed Malware Directory}\{Executed Malware Filename}.exe" --ForNetRes "FsnDCf1u1wJvLcqbFxxtOchBf2V2lgtk44oM5mt2" 0h7mFQcjRC3pDgsRcrWZ7K7bdAgvgDosJ24DmXt1 IsNotAutoStart IsNotTask
  • "{Executed Malware Directory}\{Executed Malware Filename}" --Service 1188 "FsnDCf1u1wJvLcqbFxxtOchBf2V2lgtk44oM5mt2" 0h7mFQcjRC3pDgsRcrWZ7K7bdAgvgDosJ24DmXt1
  • "{Executed Malware Directory}\{Executed Malware Filename}" --Service 1100 "FsnDCf1u1wJvLcqbFxxtOchBf2V2lgtk44oM5mt2" 0h7mFQcjRC3pDgsRcrWZ7K7bdAgvgDosJ24DmXt1
  • "%AppDataLocal%\{Hash of Machine GUID}\{Executed Malware Filename}.exe" --ForNetRes "FsnDCf1u1wJvLcqbFxxtOchBf2V2lgtk44oM5mt2" 0h7mFQcjRC3pDgsRcrWZ7K7bdAgvgDosJ24DmXt1 IsNotAutoStart IsTask
  • "%AppDataLocal%\{Hash of Machine GUID}\{Executed Malware Filename}.exe" --Service 3736 "FsnDCf1u1wJvLcqbFxxtOchBf2V2lgtk44oM5mt2" 0h7mFQcjRC3pDgsRcrWZ7K7bdAgvgDosJ24DmXt1
  • "%AppDataLocal%\{Hash of Machine GUID}\{Executed Malware Filename}.exe" --Service 2720 "FsnDCf1u1wJvLcqbFxxtOchBf2V2lgtk44oM5mt2" 0h7mFQcjRC3pDgsRcrWZ7K7bdAgvgDosJ24DmXt1
  • "%AppDataLocal%\{Hash of Machine GUID}\{Executed Malware Filename}.exe" --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, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista, 7, and 8.)

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, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista, 7, and 8.)

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}\{Executed Malware Filename}.exe" --AutoStart

Other Details

This Ransomware connects to the following possibly malicious URL:

  • http://api.{BLOCKED}a:443
  • http://{BLOCKED}d.ug/tesptc/rad/u{BLOCKED}n1.exe
  • http://loo{BLOCKED}g/hsdgfs{BLOCKED}HGhuygfuyyndfbfsbdvbsdfbsdradold/get.php?pid=B52353E3{BLOCKED}3C895678A3DFAA5E7

It adds the following scheduled tasks:

  • Task Name: Time Trigger Task
  • Schedule: At System Startup
  • Task to Run: %AppDataLocal%\{Hash of Machine GUID}\{Executed 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, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista, 7, and 8.)

Ransomware Routine

This Ransomware appends the following extension to the file name of the encrypted files:

  • .promorad2

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

  • {Encrypted Directory}\_readme.txt

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.864.05

FIRST VSAPI PATTERN DATE:

11 Mar 2019

VSAPI OPR PATTERN File:

14.865.00

VSAPI OPR PATTERN Date:

12 Mar 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

Restart in Safe Mode

[ Learn More ]

Step 4

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
    • SysHelper = "%AppDataLocal%\{Hash of Machine GUID}\{Executed Malware Filename}.exe" --AutoStart

Step 5

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.  
  • %AppDataLocal%\{Hash of Machine GUID}\{Executed Malware Filename}.exe

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

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.Win32.STOP.THCAAAI. 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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