Ransom.Win32.ENTSCRYPT.THHOAAIA

August 05, 2019
 Analysis by: Earle Maui Earnshaw
 ALIASES:

Trojan-Ransom.Win32.Gen.sds(Kaspersky); Trojan:Win32/Occamy.C(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 drops files as ransom note.

  TECHNICAL DETAILS

File Size:

1,079,808 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

31 Jul 2019

Payload:

Displays graphics/image, Displays message/message boxes

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:

  • {Encrypted Directory}{5 random characters (ext)}_Entschluesselungs_Anleitung.html → Ransom Note
  • %User Temp%\wlp.bmp → set as a desktop background as a ransom note

(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).)

Other System Modifications

This Ransomware sets the system's desktop wallpaper to the following image:

Other Details

This Ransomware does the following:

  • It avoids encrypting files with the following extensions:
    • .386
    • .adv
    • .ani
    • .bat
    • .cab
    • .cmd
    • .com
    • .cpl
    • .cur
    • .deskthemepack
    • .diagcab
    • .diagcfg
    • .diagpkg
    • .dll
    • .drv
    • .exe
    • .hlp
    • .icl
    • .icns
    • .ico
    • .ics
    • .idx
    • .ldf
    • .lnk
    • .mod
    • .mpa
    • .msc
    • .msp
    • .msstyles
    • .msu
    • .nls
    • .nomedia
    • .ocx
    • .prf
    • .psl
    • .rom
    • .rtp
    • .scr
    • .shs
    • .spl
    • .sys
    • .theme
    • .themepack
    • .wpx
    • .lock
    • .hta
    • .msi
  • It avoids encrypting files with the following file names:
    • autorun.inf
    • boot.ini
    • bootfont.bin
    • bootsect.bak
    • desktop.ini
    • iconcache.db
    • ntldr
    • ntuser.dat
    • ntuser.dat.log
    • ntuser.ini
    • bootmgr
    • bootnxt
    • thumbs.db
  • This sample does not perform encryption but rather wipes the content of the files.

Ransomware Routine

This Ransomware avoids encrypting files found in the following folders:

  • windows
  • recycle.bin
  • mozilla
  • google
  • boot
  • application data
  • appdata
  • program files
  • program files(x86)
  • programme
  • programme (x86)
  • programdata
  • perflogs
  • intel
  • msocache

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

  • {5 Random characters}

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

  • {Encrypted Directory}{5 random characters (ext)}_Entschluesselungs_Anleitung.html

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

15.272.04

FIRST VSAPI PATTERN DATE:

02 Aug 2019

VSAPI OPR PATTERN File:

15.273.00

VSAPI OPR PATTERN Date:

03 Aug 2019

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

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}{5 random characters (ext)}_Entschluesselungs_Anleitung.html
  • %User Temp%\wlp.bmp

Step 5

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.Win32.ENTSCRYPT.THHOAAIA. 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 6

Restore encrypted files from backup.

Step 7

Scan your computer with your Trend Micro product to delete files detected as Ransom.Win32.ENTSCRYPT.THHOAAIA. 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 8

Reset your Desktop properties

[ Learn More ]


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