TROJ_CRYPWALL.LC

March 07, 2015
 Analysis by: Michelle Morales
 ALIASES:

ERROR (Kaspersky); Mal/Generic-L (Sophos)

 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.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

219,678 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

07 Feb 2015

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:

  • %System Root%\{random file name}\{random file name}.exe
  • %User Profile%\Start Menu\Programs\Startup\{random file name}.exe
  • %Application Data%\{random file name}.exe

(Note: %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.. %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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 creates the following folders:

  • %System Root%\1009bbe4

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.)

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random file name} = "%System Root%\{random file name}\{random file name}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random file name} = "%Application Data%\{random file name}.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\{random 1}

HKEY_CURRENT_USER\Software\{random 1}\
01123455567789D

It adds the following registry entries:

HKEY_CURRENT_USER\Software\{random 1}
{random character}k = "-----BEGIN PUBLIC KEY----- {public key}"

HKEY_CURRENT_USER\Software\{random 1}
{random character}u = "{description of what happened to your file}"

HKEY_CURRENT_USER\Software\{random 1}
{random character}r = "{explanation of what happened to your files in HTML}"

HKEY_CURRENT_USER\Software\{random 1}
{random character}v = "[DEFAULT] BASEURL=http://paytoc4gtpn5czl2.{BLOCKED}solutions.com/{personal ID number} [InternetShortcut] URL=http://paytoc4gtpn5czl2.{BLOCKED}solutions.com/{personal ID number}"

HKEY_CURRENT_USER\Software\{random 1}\
01123455567789D
{path} = "{data}"

Dropping Routine

This Trojan drops the following files:

  • %System Root%\out.png
  • D:\{folder}\HELP_DECRYPT.TXT
  • D:\{folder}\HELP_DECRYPT.HTML
  • D:\{folder}\HELP_DECRYPT.URL
  • D:\{folder}\HELP_DECRYPT.PNG
  • C:\{folder}\HELP_DECRYPT.TXT
  • C:\{folder}\HELP_DECRYPT.HTML
  • C:\{folder}\HELP_DECRYPT.URL
  • C:\{folder}\HELP_DECRYPT.PNG

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}r.es
  • http://{BLOCKED}ia.it
  • {BLOCKED}5.164.184
  • {BLOCKED}70.88
  • {BLOCKED}167.140
  • http://{BLOCKED}consultancy.com:{port}/{random}
  • http://{BLOCKED}oard.com{port}/{random}

It deletes the initially executed copy of itself

NOTES:

This Trojan adds the following files in folders and subfolders of the root folders (i.e. C:\ and D:\):

  • HELP_DECRYPT.TXT
  • HELP_DECRYPT.HTML
  • HELP_DECRYPT.URL
  • HELP_DECRYPT.PNG

  SOLUTION

Minimum Scan Engine:

9.700

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

Delete this registry key

[ 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.

  • HKEY_CURRENT_USER\Software\{random 1}

Step 5

Delete this 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\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • 1009bbe = "%System Root%\1009bbe4\1009bbe4.exe"
  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • 1009bbe = "%Application Data%\1009bbe4.exe"

Step 6

Search and delete these components

[ Learn More ]
There may be some components 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.
  • C:\{folder}\HELP_DECRYPT.TXT
  • C:\{folder}\HELP_DECRYPT.HTML
  • C:\{folder}\HELP_DECRYPT.URL
  • C:\{folder}\HELP_DECRYPT.PNG
  • D:\{folder}\HELP_DECRYPT.TXT
  • D:\{folder}\HELP_DECRYPT.HTML
  • D:\{folder}\HELP_DECRYPT.URL
  • D:\{folder}\HELP_DECRYPT.PNG

Step 7

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %System Root%\1009bbe4

Step 8

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