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Ransom.MSIL.COBRALOCKER.AA

January 11, 2021
 Analysis by: Joshua Paul Ignacio
 ALIASES:

Trojan-Ransom.FileCrypter (IKARUS), W32/Encoder.AFA!tr (FORTINET)

 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:

Dropped by other malware


This Ransomware may be dropped by other malware.

  TECHNICAL DETAILS

File Size:

47,104 bytes

File Type:

, EXE

Memory Resident:

No

Initial Samples Received Date:

08 Jan 2021

Payload:

Displays message/message boxes, Encrypts files

Arrival Details

This Ransomware may be dropped by the following malware:

Installation

This Ransomware drops the following files:

  • %System%\LogonUI.exe

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It adds the following processes:

  • "C:\Windows\System32\cmd.exe" /takeown /f C:\Windows\System32\Taskmgr.exe && icacls C:\Windows\System32\Taskmgr.exe /grant %username%:F && del C:\Windows\System32\Taskmgr.exe && takeown /f C:\Windows\System32\LogonUI.exe && icacls C:\Windows\System32\LogonUI.exe /grant %username%:F && del C:\Windows\System32\LogonUI.exe && exit
  • "C:\Windows\System32\shutdown.exe" /r /f /t 0

Other System Modifications

This Ransomware deletes the following files:

  • %Desktop%\desktop.ini
  • %User Profile%\Downloads\desktop.ini
  • %User Profile%\Pictures\desktop.ini
  • %User Profile%\Documents\desktop.ini

(Note: %Desktop% is the current user's desktop, which is usually C:\Documents and Settings\{User Name}\Desktop on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\Desktop on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name} on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = 1

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = 1

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\Current Version\Winlogon
Shell = empty

Process Termination

This Ransomware terminates the following processes if found running in the affected system's memory:

  • cmd
  • regedit
  • Processhacker
  • sdclt
  • powershell

Other Details

This Ransomware adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System

It does the following:

  • The sample will delete the legitimate %System%\LogonUI.exe which will then be replaced by moving a dropped file %System Root%\LogonUI.exe to %System% which is responsible for displaying the following message on the screen:

    Upon clicking "Contact Us", it will display the following message:
  • It encrypts files found in the following directories:
    • %Desktop%
    • %User Profile%\Downloads
    • %User Profile%\Pictures

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

16.470.03

FIRST VSAPI PATTERN DATE:

11 Jan 2021

VSAPI OPR PATTERN File:

16.471.00

VSAPI OPR PATTERN Date:

12 Jan 2021

Step 1

Trend Micro Predictive Machine Learning detects and blocks malware at the first sign of its existence, before it executes on your system. When enabled, your Trend Micro product detects this malware under the following machine learning name:

     
    • Troj.Win32.TRX.XXPE50FFF039

Step 2

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 3

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 4

Enable Registry Editor, Task Manager, and Folder options

[ Learn More ]
By doing this step, you also enable other applications/programs disabled by this malware/grayware/spyware. Screen reader support enabled.

Step 5

Delete this registry key

[ 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.

  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System

Step 6

Restore this modified 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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\Current Version\Winlogon
    • From: Shell = empty
      To:
      Shell = {Default Value}

Step 7

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.
  • %System%\LogonUI.exe (Please make sure that the filesize is equal to 12,800 bytes or 12.5KB)

Step 8

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %Desktop%\desktop.ini
  • %User Profile%\Downloads\desktop.ini
  • %User Profile%\Pictures\desktop.ini
  • %User Profile%\Documents\desktop.ini

Step 9

Scan your computer with your Trend Micro product to delete files detected as Ransom.MSIL.COBRALOCKER.AA. 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 10

Restore encrypted files from backup.


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