Analysis by: Earle Maui Earnshaw
ALIASES:

Trojan-Ransom.Medusalocker (Ikarus)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted:

  • 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: 2,208,854 bytes
File Type: PS1
Memory Resident: Yes
Initial Samples Received Date: 17 Mar 2020

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:

  • %Application Data%\svchost.exe
  • {Encrypted File Directory}\Recovery_Instructions.html

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

It adds the following processes:

  • vssadmin.exe Delete Shadows /All /Quiet
  • bcdedit.exe /set {default} recoveryenabled No
  • bcdedit.exe /set {default} bootstatuspolicy ignoreallfailures
  • wbadmin DELETE SYSTEMSTATEBACKUP
  • wbadmin DELETE SYSTEMSTATEBACKUP -deleteOldest
  • wmic.exe SHADOWCOPY /nointeractive
  • vssadmin.exe Delete Shadows /All /Quiet
  • bcdedit.exe /set {default} recoveryenabled No
  • bcdedit.exe /set {default} bootstatuspolicy ignoreallfailures
  • wbadmin DELETE SYSTEMSTATEBACKUP
  • wbadmin DELETE SYSTEMSTATEBACKUP -deleteOldest
  • wmic.exe SHADOWCOPY /nointeractive
  • vssadmin.exe Delete Shadows /All /Quiet
  • bcdedit.exe /set {default} recoveryenabled No
  • bcdedit.exe /set {default} bootstatuspolicy ignoreallfailures
  • wbadmin DELETE SYSTEMSTATEBACKUP
  • wbadmin DELETE SYSTEMSTATEBACKUP -deleteOldest
  • wmic.exe SHADOWCOPY /nointeractive

Other System Modifications

This Ransomware adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\MDSLK
Self = powershell.exe

It modifies the following registry key(s)/entry(ies) as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
EnableLinkedConnections = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
EnableLUA = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
ConsentPromptBehaviorAdmin = 0

Other Details

This Ransomware adds the following scheduled tasks:

  • Task Name:svchost
    Task Action:%Application Data%\svchost.exe
    Task Trigger:Once installed, and every 15 minutes after indefinitely

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

Ransomware Routine

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

  • .ReadInstructions

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

  • {Encrypted File Directory}\Recovery_Instructions.html

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 15.748.03
FIRST VSAPI PATTERN DATE: 17 Mar 2020
VSAPI OPR PATTERN File: 15.749.00
VSAPI OPR PATTERN Date: 18 Mar 2020

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

To delete the added Scheduled Task file:

For Windows 7, Windows Server 2008 (R2), Windows 8, Windows 8.1, Windows 10, and Windows Server 2012 (R2):

  1. Open the Windows Task Scheduler. To do this:
    • On Windows 7, and Windows Server 2008 (R2), click Start, type taskschd.msc in the Search input field, then press Enter.
    • On Windows 8, Windows 8.1, 10 and Windows Server 2012 (R2), 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, select a Task.
  4. Check if the selected task starts the malware automatically. To do this, check the value in the Details column under the Actions tab in the lower-middle panel.
  5. If the malware path and filename are found, press DELETE and click Yes to delete the task.
  6. Repeat the steps above for the remaining tasks.

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\MDSLK

Step 6

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • From: EnableLUA = 0
      To: EnableLUA = {Default Value}
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • From: ConsentPromptBehaviorAdmin = 0
      To: ConsentPromptBehaviorAdmin = {Default Value}
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • From: EnableLinkedConnections = 1
      To: EnableLinkedConnections = {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.
  • %Application Data%\svchost.exe ? normal file copy of powershell.exe
  • {Encrypted File Directory}\Recovery_Instructions.html ? ransom notes

Step 8

Enabling Windows Error Recovery

  1. Run the command prompt (cmd.exe) as administrator.
  2. Enable Windows Error Recovery Screen on Startup by typing the following command:
    bcdedit /set {default} bootstatuspolicy displayallfailures

Step 9

Enabling Startup Repair

  1. Run the command prompt (cmd.exe) as administrator.
  2. Enable Startup Repair by typing the following command:
    /bcedit /set {default} recoveryenabled Yes

Step 10

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.PS1.MEDUSALOCKER.B. 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 11

Restore encrypted files from backup.


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