Analysis by: John Karlo Agon
ALIASES:

Trojan.Cryptodefense (Symantec), Ransom:Win32/Crowti.A (Microsoft), TR/Crypt.ZPACK.11520 (Avira), Inject2.CLSW (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.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 229,376 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 13 Jul 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 8 Characters}\{Random 8 Characters}.exe
  • %Application Data%\{Random 8 Characters}.exe
  • %User Startup%\{Random 8 Characters}.exe

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %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.. %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

It drops the following files:

  • %User Startup%\HELP_DECRYPT.HTML
  • %User Startup%\HELP_DECRYPT.PNG
  • %User Startup%\HELP_DECRYPT.TXT
  • %User Startup%\HELP_DECRYPT.URL

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

It drops and executes the following files:

  • %Desktop%\HELP_DECRYPT.HTML
  • %Desktop%\HELP_DECRYPT.PNG
  • %Desktop%\HELP_DECRYPT.TXT
  • %Desktop%\HELP_DECRYPT.URL

(Note: %Desktop% is the desktop folder, where it usually is C:\Documents and Settings\{user name}\Desktop in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\Desktop in 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%\{Random 8 Characters}

(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:

HKCU\Software\Microsoft\
Windows\CurrentVersion\Run
{First 7 Characters of {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"

HKCU\Software\Microsoft\
Windows\CurrentVersion\RunOnce - (Windows Vista or higher)
{Last 7 Characters of {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"

HKCU\Software\Microsoft\
Windows\CurrentVersion\Run
{Random 8 Characters} = "%Application Data%\{Random 8 Characters}.exe"

HKCU\Software\Microsoft\
Windows\CurrentVersion\RunOnce - (Windows Vista or higher)
{Random 8 Characters} = "%Application Data%\{Random 8 Characters}.exe"

It drops the following file(s) in the Windows Startup folder to enable its automatic execution at every system startup:

  • %User Startup%\{Random 8 Characters}.exe

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

Other System Modifications

This Trojan adds the following registry keys:

HKCU\Software\{Random 32 Characters}

HKCU\Software\{Random 32 Characters}\
{Random 16 Characters}

It adds the following registry entries:

HKCU\Software\{Random 32 Characters}
{random 2 characters} = "{hex value}"

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}og.co.za/aa.php
  • http://{BLOCKED}o.com/wp-content/plugins/woocommerce-one-click/vendor/stripe/stripe-php/lib/Error/ee.php
  • http://{BLOCKED}hsolutions.com/wp-includes/js/tinymce/themes/advanced/skins/o2k7/img/dd.php
  • http://{BLOCKED}g.pamieciprzyszlosc.pl/wp-includes/js/tinymce/plugins/cc.php
  • http://{BLOCKED}as.net/wp-content/plugins/bb.php
  • http://{BLOCKED}estorationpros.com/wp-content/plugins/ee.php
  • www.{BLOCKED}anty.com/wp-content/themes/dd.php
  • http://{BLOCKED}viciossas.net/wp-includes/cc.php
  • http://{BLOCKED}e.8z.com/wp-content/uploads/updatedmaps/Arvada/Old%20Arvada.bb.php
  • http://{BLOCKED}form.com.sg/staging/wp-includes/aa.php
  • http://{BLOCKED}-healthcare-management-for-leaders.com/bemerkenswert/wp-content/ee.php
  • http://{BLOCKED}uadalajara.org/wp-content/plugins/dd.php
  • http://{BLOCKED}rsscandal.com/wp-content/themes/cc.php
  • http://{BLOCKED}a-biografikwn.com/wp-content/plugins/bb.php
  • http://{BLOCKED}nmasonry.com/wp-includes/aa.php
  • http://{BLOCKED}lesschoolcentral.org/dir/wp-content/ee.php
  • http://{BLOCKED}redservices.org.uk/wp-content/plugins/dd.php
  • http://{BLOCKED}uresandtrips.com/wp-content/plugins/cc.php
  • http://{BLOCKED}ial.trapponline.com/wp-content/plugins/bb.php
  • http://{BLOCKED}xp.com/starcraft2guides/wp-content/plugins/aa.php
  • http://{BLOCKED}ion.co.uk/wp-content/uploads/2015/03/update-a9afa977161aa75fe3a7b760b1051876/tmp/ee.php
  • http://{BLOCKED}-central.de/piwik/core/Tracker/Db/Pdo/dd.php
  • http://{BLOCKED}illiams.com.au/wp-content/cc.php
  • http://{BLOCKED}4.com/news3/wp-includes/bb.php
  • http://{BLOCKED}smilesofhamden.com/wp-content/aa.php
  • http://{BLOCKED}girlphotography.com/wp-includes/ee.php
  • http://{BLOCKED}u.co.uk/wp-includes/dd.php
  • http://{BLOCKED}ic.co.za/cc.php
  • http://{BLOCKED}lhealthinternational.com/sgsbeautify.com/wp-content/bb.php
  • http://{BLOCKED}atone.com/wp-content/plugins/aa.php
  • http://{BLOCKED}immer.nl/wp-content/themes/dd.php
  • http://{BLOCKED}potolkov12.ru/wp-content/plugins/cc.php
  • http://{BLOCKED}nc.com/wp-content/plugins/bb.php
  • http://{BLOCKED}-jones.co.nz/wp-includes/js/tinymce/plugins/aa.php

It deletes itself after execution.

NOTES:

It is capable of encrypting files in the affected system.

It drops HELP_DECRYPT.HTML, HELP_DECRYPT.PNG, HELP_DECRYPT.TXT, and HELP_DECRYPT.URL to the folders where it tries to encrypt the files.

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.790.03
FIRST VSAPI PATTERN DATE: 14 Jul 2015
VSAPI OPR PATTERN File: 11.791.00
VSAPI OPR PATTERN Date: 15 Jul 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

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.

  • In HKEY_CURRENT_USER\Software
    • {Random 32 Characters}

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
    • {First 7 Characters of {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {Random 8 Characters} = "%Application Data%\{Random 8 Characters}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce - (Windows Vista or higher)
    • {Last 7 Characters of {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce - (Windows Vista or higher)
    • {Random 8 Characters} = "%Application Data%\{Random 8 Characters}.exe"

Step 6

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 Startup%\HELP_DECRYPT.HTML
  • %User Startup%\HELP_DECRYPT.PNG
  • %User Startup%\HELP_DECRYPT.TXT
  • %User Startup%\HELP_DECRYPT.URL
  • %Desktop%\HELP_DECRYPT.HTML
  • %Desktop%\HELP_DECRYPT.PNG
  • %Desktop%\HELP_DECRYPT.TXT
  • %Desktop%\HELP_DECRYPT.URL
  • In the Look In drop-down list, select My Computer then press Enter.
  • Once located, select the file then press SHIFT+DELETE to delete it.
    *Note: The file name input box title varies depending on the Windows version (e.g. Search for files or folders named or All or part of the file name.).

    • • For Windows Vista, Windows 7, Windows Server 2008, Windows 8, Windows 8.1, and Windows Server 2012:

    1. Open a Windows Explorer window.
      • For Windows Vista, 7, and Server 2008 users, click Start>Computer.
      • For Windows 8, 8.1, and Server 2012 users, right-click on the lower left corner of the screen, then click File Explorer.
    2. In the Search Computer/This PC input box, type:
      • %User Startup%\HELP_DECRYPT.HTML
      • %User Startup%\HELP_DECRYPT.PNG
      • %User Startup%\HELP_DECRYPT.TXT
      • %User Startup%\HELP_DECRYPT.URL
      • %Desktop%\HELP_DECRYPT.HTML
      • %Desktop%\HELP_DECRYPT.PNG
      • %Desktop%\HELP_DECRYPT.TXT
      • %Desktop%\HELP_DECRYPT.URL
  • Once located, select the file then press SHIFT+DELETE to delete it.
    *Note: Read the following Microsoft page if these steps do not work on Windows 7.

    • 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%\{Random 8 Characters}

    Step 8

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