TROJ_CRYPCTB.YVV

 Analysis by: Ryan Gardo

 ALIASES:

MSIL7.BRLS (AVG), Gen:Variant.Kazy.596255 (BitDefender), Ransom:Win32/Critroni.B (Microsoft)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware


This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It uses Windows Task Scheduler to create a scheduled task that executes the dropped copy.

It connects to certain websites to send and receive information.

  TECHNICAL DETAILS

File Size:

1,327,104 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

21 Apr 2015

Payload:

Drops files, Modifies files, Encrypts files

Arrival Details

This Trojan 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 Trojan drops the following copies of itself into the affected system and executes them:

  • %User Temp%\{random filename1}.exe

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

It drops the following files:

  • %Windows%\Tasks\{random filename2}.job
  • %System Root%\{randomly selected path}!Decrypt-All-Files-{random 7 letters}.txt - ransom note
  • %System Root%\{randomly selected path}!Decrypt-All-Files-{random 7 letters}.bmp - image of wallpaper
  • %ALL Users Profile%\Application Data\{random file name3}.html - contains the list of encrypted files
  • %User Profile%\My Documents\!Decrypt-All-Files-{random 7 letters}.txt - ransome note.
  • %User Profile%\My Documents\!Decrypt-All-Files-{random 7 letters}.bmp - image used as wallpaper.

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.. %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

It uses Windows Task Scheduler to create a scheduled task that executes the dropped copy.

Autostart Technique

The scheduled task executes the malware every:

  • at logon

Other System Modifications

This Trojan modifies the following registry entries:

HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = %User Profile%\My Documents\!Decrypt-All-Files-{random 7 letters}.bmp

(Note: The default value data of the said registry entry is {User Defined}.)

HKEY_CURRENT_USER\Control Panel\Desktop
TileWallpaper = "0"

(Note: The default value data of the said registry entry is "User Defined".)

HKEY_CURRENT_USER\Control Panel\Desktop
WallpaperStyle = "0"

(Note: The default value data of the said registry entry is "User Defined".)

Other Details

This Trojan connects to the following URL(s) to get the affected system's IP address:

  • http://ip.telize.com

It connects to the following website to send and receive information:

  • http://{BLOCKED}mxlqabmvfnw4wp4.onion.lt
  • http://{BLOCKED}mxlqabmvfnw4wp4.tor2web.fi
  • http://{BLOCKED}mxlqabmvfnw4wp4.onion.cab
  • http://{BLOCKED}mxlqabmvfnw4wp4.onion.gq
  • http://{BLOCKED}mxlqabmvfnw4wp4.tor2web.org
  • http://{BLOCKED}mxlqabmvfnw4wp4.tor2web.blutmagie.de

It encrypts files with the following extensions:

  • 3fr
  • 7z
  • accdb
  • ai
  • arw
  • bas
  • bay
  • blend
  • cdr
  • cer
  • cpp
  • cr2
  • crt
  • c
  • crw
  • cs
  • db
  • dbf
  • dcr
  • dds
  • dd
  • der
  • dng
  • docm
  • docx
  • doc
  • dwg
  • dxf
  • dxg
  • eps
  • erf
  • groups
  • indd
  • jpe
  • jpeg
  • jpg
  • js
  • kdc
  • kwm
  • mdb
  • mdf
  • md
  • mef
  • mrw
  • nef
  • nrw
  • odb
  • odm
  • odp
  • ods
  • odt
  • orf
  • p12
  • p7b
  • p7c
  • pdd
  • pdf
  • pef
  • pem
  • pfx
  • php
  • pl
  • pptm
  • ppt
  • pptx
  • psd
  • pst
  • ptx
  • pwm
  • py
  • r3d
  • raf
  • rar
  • raw
  • rtf
  • rw2
  • rwl
  • safe
  • sql
  • srf
  • srw
  • txt
  • vsd
  • wb2
  • wpd
  • wps
  • xlk
  • xlsm
  • xls
  • xlsb
  • xlsx
  • zip

It renames encrypted files using the following names:

  • {original file name and extension}.{random 7 letters}

NOTES:

The dropped !Decrypt-All-Files-{random 7 letters}.tx contains the following ransom message:

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

It displays the following ransom message: The ransom message can be viewed in 7 different languages: French, Spanish, Austrian, German, Dutch, Italian and English

It allows the user to decrypt up to five files for free:

It asks the user to pay via Bitcoin payment:

If the connection is not established, it will instruct the user on how to pay the ransom in another computer with an internet connection.

It deletes copies of itself and its scheduled task after the time expired.

  SOLUTION

Minimum Scan Engine:

9.750

FIRST VSAPI PATTERN FILE:

11.616.04

FIRST VSAPI PATTERN DATE:

15 Apr 2015

VSAPI OPR PATTERN File:

11.617.00

VSAPI OPR PATTERN Date:

16 Apr 2015

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 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

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_CURRENT_USER\Control Panel\Desktop
    • From: TileWallpaper = "0"
      To: TileWallpaper = "{User-defined}"
  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • From: WallpaperStyle = "0"
      To: WallpaperStyle = "{User-defined}"
  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • From: Wallpaper = "C:\Documents and Settings\winxp.KARLD-WINXP\My Documents\!Decrypt-All-Files-{random 7 letters}.bmp"
      To: Wallpaper = "{User-defined}"

Step 5

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.
  • %Windows%\Tasks\{random filename2}.job
  • %System Root%\{randomly selected path}!Decrypt-All-Files-{random 7 letters}.txt
  • %System Root%\{randomly selected path}!Decrypt-All-Files-{random 7 letters}.bmp
  • %ALL Users Profile%\Application Data\{random file name3}.html
  • %User Profile%\My Documents\!Decrypt-All-Files-{random 7 letters}.txt
  • %User Profile%\My Documents\!Decrypt-All-Files-{random 7 letters}.bmp

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_CRYPCTB.YVV. 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.

NOTES:

Restore the encrypted files by this malware from backup. Note that the encrypted files have the extension .{random 7 letters}.


Did this description help? Tell us how we did.