TROJ_CRYPCTB.J

 Analysis by: Michelle Morales

 ALIASES:

VirTool:Win32/CeeInject.gen!KK (Microsoft), Trojan.Win32.Inject.tpsl (Kaspersky), a variant of Win32/Injector.BRCN trojan (ESET)

 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.

  TECHNICAL DETAILS

File Size:

1,031,726 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

12 Dec 2014

Payload:

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 files:

  • %User Profile%\My Documents\Decrypt All Files {random characters}.bmp - image used as wallpaper
  • %User Profile%\My Documents\Decrypt All Files {random characters}.txt - ransom note in text file
  • %User Profile%\My Documents\{random characters}.html - contains ransom note and list of encrypted files

(Note: %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 drops the following copies of itself into the affected system:

  • %User Temp%\{random filename}.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.)

Autostart Technique

This Trojan drops the following files:

  • C:\Windows\Tasks\{random filename}.job

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 characters}.bmp"

(Note: The default value data of the said registry entry is {user-defined}.)

Other Details

This Trojan encrypts files with the following extensions:

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

NOTES:

The dropped Decrypt All Files {random characters}.txt contains the following ransom message:

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

It appends the extension .{7 random characters} to the encrypted files.

It displays the following ransom message:

It asks for users to connect to the given URLs to pay and retrieve the key for decryption.

  SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

11.340.04

FIRST VSAPI PATTERN DATE:

12 Dec 2014

VSAPI OPR PATTERN File:

11.341.00

VSAPI OPR PATTERN Date:

13 Dec 2014

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

Scan your computer with your Trend Micro product and note files detected as TROJ_CRYPCTB.J

Step 4

Restart in Safe Mode

[ Learn More ]

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.  
  • %User Profile%\My Documents\Decrypt All Files {random characters}.bmp
  • %User Profile%\My Documents\Decrypt All Files {random characters}.txt
  • %User Profil%\My Documents\{random characters}.html
  • %Windows%\Tasks\{random filename}.job

Step 6

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • From: Wallpaper = "%User Profile%\My Documents\Decrypt All Files {random characters}.bmp"
      To: Wallpaper = "{user-defined}"

Step 7

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


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