Analysis by: Jemuel Igadna
ALIASES:

a variant of Win32/Filecoder.Nokoyawa.D trojan(NOD32)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

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: 44,544 bytes
File Type: EXE
Memory Resident: No
Payload: Encrypts files, Modifies system registry

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 adds the following processes:

  • if --safe-mode commandline parameter is used:
    • "%System%\bcdedit.exe" /set {default} safeboot network
    • "%System%\shutdown.exe" -r

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

Autostart Technique

This Ransomware registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control\SafeBoot\Network\
nokonoko → if --safe-mode commandline parameter is used.

Other System Modifications

This Ransomware modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control
ServicesPipeTimeout = 86400000 → if --safe-mode commandline parameter is used.

Other Details

This Ransomware does the following:

  • It encrypts files found in the following drives:
    • Fixed Drives
    • Removable Drives
    • Remote (Network) Drives
  • The following can be changed in the runtime configuration:
    • Appended extension on encrypted files
    • Ransom note filename
    • Ransom note content
    • ECC key
    • Directories to avoid
    • File extensions to avoid
  • The following can be enabled/disabled in the runtime configuration:
    • Encryption of network shares
    • Deletion of shadow copies
    • Loading of hidden drives
  • It adds the following services if --safe-mode commandline parameter is used:
      Service Name: nokonoko
      Display Name: shmokoshmoko
      Image Path: {Malware File Path}\{Malware File Name}.{Malware File Extension} --config --safe-mode

It accepts the following parameters:

  • --config {Base64 encoded config} → runtime configuration of the sample
  • --dir → encrypt selected directories and sub-directories
  • --file → encrypt selected files
  • --safe-mode → reboots and encrypts the user's machine in safe mode
  • --debug
  • --verbose

Ransomware Routine

This Ransomware drops the following file(s) as ransom note:

  • {Encrypted Directory}\{File Name Specified in Base64 Encrypted Config}.txt

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 18.550.02
FIRST VSAPI PATTERN DATE: 05 Jul 2023
VSAPI OPR PATTERN File: 18.551.00
VSAPI OPR PATTERN Date: 06 Jul 2023

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.XXPE50FFF069

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

Restart in Safe Mode

[ Learn More ]

Step 5

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\SYSTEM\ControlSet001\Control
    • ServicesPipeTimeout = 86400000

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_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\SafeBoot\Network\nokonoko

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.
  • {Encrypted Directory}\{File Name Specified in Base64 Encrypted Config}.txt

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.Win32.NOKO.YXDGET. 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 9

Restore encrypted files from backup.


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