Analysis by: Jay Bradley Nebre
ALIASES:

Ransom:Win32/Filecoder.PD!MTB(Microsoft)

 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: Dropped by other malware, 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 deletes itself after execution.

It encrypts files with specific file extensions. It drops files as ransom note. It avoids encrypting files with the following file extensions.

  TECHNICAL DETAILS

File Size: 516,608 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 19 Mar 2020
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 and executes the following files:

  • %User Temp%\update.bat - deletes the malware sample

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

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

  • Pysa

Other System Modifications

This Ransomware adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
legalnoticetext = {Ransom Note Message}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
legalnoticecaption = PYSA

Other Details

This Ransomware deletes itself after execution.

Ransomware Routine

This Ransomware encrypts files with the following extensions:

  • .doc
  • .xls
  • .docx
  • .xlsx
  • .pdf
  • .db
  • .db3
  • .frm
  • .ib
  • .mdf
  • .mwb
  • .myd
  • .ndf
  • .sdf
  • .sql
  • .trc
  • .wrk
  • .001
  • .acr
  • .bac
  • .bak
  • .backupdb
  • .bck
  • .bkf
  • .bkup
  • .bup
  • .fbk
  • .mig
  • .spf
  • .vhdx
  • .vfd
  • .avhdx
  • .vmcx
  • .vmrs
  • .pbf
  • .qic
  • .sqb
  • .tis
  • .vbk
  • .vbm
  • .vrb
  • .win
  • .sql
  • .pst
  • .mdb
  • .7z
  • .zip
  • .rar
  • .cad
  • .dsd
  • .dwg
  • .pla
  • .pln

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

  • ":\Windows\"
  • "\Boot\"
  • "\BOOTSECT"
  • "\pagefile"
  • "\System Volume Information\"
  • "bootmgr"
  • "\Recovery"
  • "\Microsoft"
  • ":\Windows\"
  • "\Boot\"
  • "\BOOTSECT"
  • "\pagefile"
  • "\System Volume Information\"
  • "bootmgr"
  • "\Recovery"
  • "\Microsoft"

It appends the following extension to the file name of the encrypted files:

  • .pysa

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

  • {Encrypted Folder}\Readme.README

It avoids encrypting files with the following file extensions:

  • .exe
  • .dll
  • .README
  • .pysa
  • .search-ms
  • .sys

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 15.650.05
FIRST VSAPI PATTERN DATE: 29 Jan 2020
VSAPI OPR PATTERN File: 15.651.00
VSAPI OPR PATTERN Date: 30 Jan 2020

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.XXPE50FFF034

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

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • legalnoticetext = {Ransom Note Message}
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • legalnoticecaption = PYSA

Step 6

Restore encrypted files from backup.

Step 7

Scan your computer with your Trend Micro product to delete files detected as Ransom.Win32.MESPINOZA.SMDA. 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:


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