Analysis by: Thea Patrice Tajonera
ALIASES:

Trojan-Ransom.FileCrypter (IKARUS); BAT/Filecoder.DW trojan (NOD32)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: Yes

  • 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 encrypts files with specific file extensions. It drops files as ransom note.

  TECHNICAL DETAILS

File Size: 395,776 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 23 Mar 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 adds the following folders:

  • %User Temp%\{4 Random Characters}.tmp -> deleted afterwards
  • %User Temp%\{4 Random Characters}.tmp\{4 Random Characters}.tmp -> deleted afterwards

(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 drops the following files:

  • %User Temp%\{4 Random Characters}.tmp\{4 Random Characters}.tmp\{4 Random Characters}.bat -> deleted afterwards
  • %User Temp%\{4 Random Characters}.tmp\aescrypt.exe -> used for file encryption
  • %Application Data%\inf.bmp-> used as wallpaper
    • Originally %User Temp%\{4 Random Characters}.tmp\photo.bmp
  • %User Profile%\oid.txt -> contains victim's ID key

(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).. %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).. %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).)

It adds the following processes:

  • "%System%\cmd.exe" /c "%User Temp%\{4 Random Characters}.tmp\{4 Random Characters}.tmp\{4 Random Characters}.bat {Malware Path}\{Malware Filename{.exe"
  • vssadmin delete shadows /quiet /all
  • wmic.exe shadowcopy delete
  • wbadmin delete catalog /quiet
  • aescrypt.exe -e -p "{Encryption Key}" {File to encrypt} -> file encryption routine
  • certutil /encode "%User Temp%\key.txt" "%User Profile%\oid.txt"
  • reg add "HKEY_CURRENT_USER\Control Panel\Desktop" /v Wallpaper /t REG_SZ /d %Application Data%\inf.bmp /f
  • RUNDLL32.EXE user32.dll,UpdatePerUserSystemParameters

(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).. %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).. %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).)

Other System Modifications

This Ransomware changes the desktop wallpaper by modifying the following registry entries:

HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = %Application Data%\inf.bmp /f

It sets the system's desktop wallpaper to the following image:

Other Details

This Ransomware does the following:

  • The dropped batch file is used for file encryption and contains commands to remove shadow copies

Ransomware Routine

This Ransomware encrypts files with the following extensions:

  • .txt
  • .png
  • .doc
  • .docx
  • .jpg
  • .jpeg
  • .webp
  • .tif
  • .tiff
  • .ps
  • .zip
  • .rar
  • .7z
  • .z
  • .iso
  • .img
  • .cpp
  • .cs
  • .php
  • .py
  • .rtf
  • .log
  • .dic
  • .dot
  • .wbk
  • .docm
  • .dotx
  • .dotm
  • .docb
  • .xls
  • .xlt
  • .xlm
  • .xlsx
  • .xltx
  • .xltm
  • .xlsb
  • .xla
  • .xlam
  • .xll
  • .xlw
  • .ppt
  • .pot
  • .pps
  • .pptx
  • .pptm
  • .potx
  • .potm
  • .ppam
  • .ppsx
  • .ppsm
  • .sldx
  • .sldm
  • .ACCDB
  • .ACCDE
  • .ACCDT
  • .ACCDR
  • .one
  • .pub
  • .xps
  • .raw
  • .gif
  • .bmp
  • .eps
  • .cr2
  • .nef
  • .orf
  • .sr2
  • .pdf
  • .ai
  • .psd
  • .indd
  • .mp3
  • .mp4
  • .ico
  • .ogg
  • .avi
  • .svg
  • .djvu
  • .m4a
  • .flac
  • .fb2
  • .wav
  • .wma
  • .wbk
  • .aac
  • .mpeg
  • .mov
  • .wmv
  • .flv
  • .AVCHD
  • .webm
  • .mkv
  • .epub
  • .odt
  • .jpe
  • .jfif
  • .dvs
  • .java
  • .pyw
  • .pyc
  • .pas
  • .c
  • .p
  • .swf
  • .jsp
  • .jspx
  • .wss
  • .pl
  • .phtml
  • .rb
  • .rhtml
  • .cgi
  • .bas
  • .dvs
  • .sql
  • .4dd
  • .4dl
  • .adb
  • .ade
  • .adf
  • .adp
  • .alf
  • .ask
  • .btr
  • .cat
  • ,cdb
  • .ckp
  • .cma
  • .cpd
  • .dacpac
  • .dad
  • .dadiagrams
  • .daschema
  • .db-shm
  • .db-wal
  • .db3
  • .dbc
  • .sis
  • .sqlite
  • .sqlite3
  • .sqlitedb
  • .tga
  • .dfm
  • .msppr
  • .3mf
  • .asm
  • .acs
  • .jar
  • .ace
  • .arj
  • .cab
  • .gz
  • .gzip
  • .pak
  • .pkg
  • .rpm
  • .sh
  • .sib
  • .sisx
  • .sit
  • .sitx
  • .spl
  • .tar
  • .tar-gz
  • .tgz
  • .xar
  • .zipx
  • .0
  • .000
  • .001
  • .a00
  • .a01
  • .a02
  • .ain
  • .rz
  • .tg
  • .123
  • .csv
  • .ViR
  • .tg
  • .pfx
  • .key
  • .no_more_ransom
  • .crt
  • .csr
  • .bak
  • .WCRY
  • .db
  • .css
  • .js
  • .15nhqv65m
  • .saga
  • .Cerber2
  • .Cerber3
  • .cerber
  • .126-D7C-E67
  • .__NIST_K571__
  • .ctbl
  • .text
  • .dnproject
  • .ods
  • .wpd
  • .CHAVO
  • .lzh
  • .1st
  • .600
  • .602
  • .abw
  • .acl
  • .afp
  • .ami
  • .ans
  • .asc
  • .aww
  • .ccf
  • .cwk
  • .dbk
  • .dita
  • .dwd
  • .eggt
  • .ezw
  • .fdx
  • .ftm
  • .ftx
  • .gdoc
  • .hwp
  • .hwpml
  • .lwp
  • .mbp
  • .md
  • .me
  • .mcw
  • .mobi
  • .nb
  • .nbp
  • .neis
  • .nt
  • .nq
  • .nes
  • .odoc
  • .osheet
  • .itt
  • .j
  • .f90
  • .go
  • .kts
  • .ky
  • .ktm
  • .scala
  • .sc
  • .hs
  • .hoi1
  • .joi2
  • .hoi3
  • .hoi4
  • .save
  • .ais
  • .0adsave
  • .32x
  • .3ds
  • .mod
  • .3dsx
  • .3dz
  • .555
  • .68k
  • .8ld
  • .a26
  • .a52
  • .aao
  • .abk
  • .ac
  • .acf
  • .acww
  • .acx
  • .adf
  • .adt
  • .air
  • .am1
  • .gfx
  • .yml
  • .dds
  • .bz2
  • .lz
  • .uue
  • .xz
  • .zipx
  • .gdcb
  • .gesd
  • .602
  • .7-zip
  • .act
  • .aim
  • .adoc
  • .ans
  • .apkg
  • .ascii
  • .ase
  • .aty
  • .awp
  • .aww
  • .lzma
  • .axx
  • .ccc
  • .swift
  • .uot
  • .sb
  • .lnk
  • .rbxl
  • .iss
  • .ino
  • .arsc
  • .pjx
  • .rpy
  • .vcproj
  • .in
  • .awk
  • .rbxm
  • .gitignore
  • .xap
  • .sln
  • .b
  • .proto
  • .vbp
  • .smali
  • .swc

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

  • {Original Filename}.{Original Extension}.aes

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

  • {Encrypted Directory}\Readme.txt
  • %System Root%\Readme.txt

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 16.612.06
FIRST VSAPI PATTERN DATE: 23 Mar 2021
VSAPI OPR PATTERN File: 16.613.00
VSAPI OPR PATTERN Date: 24 Mar 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.XXPE50FFF042

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

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.
  • %User Temp%\{4 Random Characters}.tmp\aescrypt.exe
  • %Application Data%\inf.bmp
  • %User Profile%\oid.txt
  • {Encrypted Directory}\Readme.txt
  • %System Root%\Readme.txt

Step 5

Reset your Desktop properties

[ Learn More ]

Step 6

Scan your computer with your Trend Micro product to delete files detected as Ransom.Win32.ONIM.THCBCBA. 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 7

Restore encrypted files from backup.


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