Analysis by: Karen Ivy Titiwa
ALIASES:

Ransom:MSIL/Cobra.PA!MTB(MICROSOFT); TrojanRansom.MSIL(QUICKHEAL)

 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 encrypts files found in specific folders.

  TECHNICAL DETAILS

File Size: 138,752 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 07 Jan 2021
Payload: Displays message/message boxes, Encrypts files

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:

  • C:\Windows\System32LogonUI.exe
  • C:\Windows\System32\LogonUI.exe

It adds the following processes:

  • cmd.exe /k color 47 && takeown /f C:\Windows\System32\LogonUI.exe && icacls C:\Windows\System32\LogonUI.exe /grant %username%:F && copy C:\Windows\System32\LogonUI.exe %temp%\LogonUI.exe && del C:\Windows\System32\LogonUI.exe && takeown /f C:\Windows\System32\Taskmgr.exe && icacls C:\Windows\System32\Taskmgr.exe /grant %username%:F && del C:\Windows\System32\Taskmgr.exe && exit

Other System Modifications

This Ransomware deletes the following files:

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

(Note: %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).)

Other Details

This Ransomware adds the following registry keys:

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

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "empty"

It does the following:

  • Computes for the hash value of "DaVinci" and uses it in its encryption routine
  • Hides the window of the following running processes:
    • cmd
    • regedit
    • Processhacker
    • sdclt
    • powershell
  • It displays the following as ransom note:
  • When a correct code is provided
    • It displays the following:
    • Decrypt files stored in
      • %User Profile%\Desktop
      • %User Profile%\Downloads
      • %User Profile%\Pictures
    • It executes the following command
      • "cmd.exe /del C:\Windows\System32\LogonUI.exe && copy %temp%\LogonUI.exe C:\Windows\System32\LogonUI.exe && exit"
    else
    • It displays the following:
  • Accepts "DaVinci" as the correct code

Ransomware Routine

This Ransomware encrypts files found in the following folders:

  • %User Profile%\Desktop
  • %User Profile%\Downloads
  • %User Profile%\Pictures

(Note: %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).)

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 16.472.04
FIRST VSAPI PATTERN DATE: 12 Jan 2021
VSAPI OPR PATTERN File: 16.473.00
VSAPI OPR PATTERN Date: 13 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

Identify and terminate files detected as Ransom.MSIL.COBRALOCKER.C

[ 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 5

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 6

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.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • DisableTaskMgr = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • DisableRegistryTools = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Shell = empty

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.
  • C:\Windows\System32LogonUI.exe
  • C:\Windows\System32\LogonUI.exe

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.

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

Step 9

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