Analysis by: Francis Xavier Antazo

ALIASES:

Ransom:Win32/Critroni(MICROSOFT), Win32/Filecoder.DA trojan(NOD32), Trojan horse FileCryptor.LJ(AVG)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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: 1,153,032 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 09 Oct 2014

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\AllFilesAreLocked {Random Numbers 1}.bmp
  • %User Profile%\My Documents\DecryptAllFiles {Random Numbers 1}.txt
  • %User Profile%\My Documents\{Random Filename}.html
  • %Windows%\Tasks\{Random Filename 2}.job

(Note: %User Profile% is a user's profile folder, where it usually is C:\Documents and Settings\{user name} on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name} 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.. %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

It drops the following copies of itself into the affected system:

  • %User Temp%\{Random Filename 1}.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.)

Other System Modifications

This Trojan modifies the following registry entries:

HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = "%User Profile%\My Documents\AllFilesAreLocked {Random Numbers 1}.bmp"

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

Mobile Malware Routine

This Trojan accesses the following possibly malicious URL(s):

  • {BLOCKED}c2kaceyufw.onion.cab

NOTES:
It appends {random file extension} to the encrypted files.

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 11.158.02
FIRST VSAPI PATTERN DATE: 19 Sep 2014
VSAPI OPR PATTERN File: 11.159.00
VSAPI OPR PATTERN Date: 20 Sep 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

Identify and terminate files detected as TROJ_CRYPCTB.C

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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: Wallpaper = "%User Profile%\My Documents\AllFilesAreLocked {Random Numbers 1}.bmp"
      To: Wallpaper = "{User Preference}"

Step 5

Search and delete these files

[ 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\AllFilesAreLocked {Random Numbers 1}.bmp
  • %User Profile%\My Documents\DecryptAllFiles {Random Numbers 1}.txt
  • %User Profile%\My Documents\{Random Filename 1}.html
  • %Windows%\Tasks\{Random Filename 2}.job

Step 6

Scan your computer with your Trend Micro product to delete files detected as TROJ_CRYPCTB.C. 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.


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