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Ransom.Win32.RYUK.THDBEAI

May 14, 2019
 Modified by: Earle Maui Earnshaw
 ALIASES:

Trojan-Ransom.Win32.Encoder.aca(Kaspersky); Trojan:Win32/Occamy.B!bit (Microsoft)

 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

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:

122,368 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

09 May 2019

Payload:

Connects to URLs/IPs, Encrypts 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 files:

  • %Public%\sys

(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:

  • %system%\cmd.exe /c reg add hkey_current_user\software\microsot\windows\currentversion\run /v svchos /t reg_sz /d {malware path and file name} /f

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

  • FakeMutex

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
svchos = "{malware path and file name}.exe"

Other Details

This Ransomware does the following:

  • It only encrypts Fixed Drives
  • Checks for all running processes and creates a remote thread to all running processes except the following:
    • {Malware File Name}.exe
    • csrss.exe
    • explorer.exe
    • lsaas.exe
  • Avoids encrypting the following file extensions:
    • dll
    • DLL
    • lnk
    • LNK
    • hrmlog
    • HRMLOG
    • ini
    • INI
    • exe
    • EXE

Ransomware Routine

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

  • Windows
  • AhnLab
  • Chrome
  • Mozilla
  • $Recycle.Bin
  • WINDOWS

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

  • {Encrypted Directory}\RyukReadMe.txt

It leaves text files that serve as ransom notes containing the following text:

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.946.06

FIRST VSAPI PATTERN DATE:

18 Apr 2019

VSAPI OPR PATTERN File:

14.947.00

VSAPI OPR PATTERN Date:

19 Apr 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
    • svchos = "{Malware path and name}.exe"

Step 5

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.
  • %Public%\sys
  • {Encrypted Directory}\RyukReadMe.txt

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.Win32.RYUK.THDBEAI. 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 7

Restore encrypted files from backup.


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