TROJ_CRYPWALL.RUI

 Analysis by: Anthony Joe Melgarejo

 ALIASES:

Ransom:Win32/Crowti.A (Microsoft); Trojan.Cryptodefense (Symantec), Trojan.CryptoWall (Malwarebytes)

 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:

348,339 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

03 Aug 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:\Documents and Settings\{user}\Start Menu\Programs\Startup on Windows 2000 and XP, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup on Windows Vista, 7, and 8.)

It drops the following files:

  • %Desktop%\HELP_DECRYPT.HTML
  • %Desktop%\HELP_DECRYPT.PNG
  • %Desktop%\HELP_DECRYPT.TXT
  • %Desktop%\HELP_DECRYPT.URL
  • %User Startup%\HELP_DECRYPT.HTML
  • %User Startup%\HELP_DECRYPT.PNG
  • %User Startup%\HELP_DECRYPT.TXT
  • %User Startup%\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.. %User Startup% is the current user's Startup folder, which is usually C:\Documents and Settings\{user}\Start Menu\Programs\Startup on Windows 2000 and XP, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup on Windows Vista, 7, and 8.)

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 7 characters} = "%System Root%\{random 8 characters}\{random 8 characters}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random 8 characters} = "%Application Data%\{random 8 characters}.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\{UID}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\{UID}
{random 2 characters} = "{RSA PUBLIC KEY} "

HKEY_CURRENT_USER\Software\{UID}
{random 2 characters} = "{contents of HELP_DECRYPT.TXT}"

HKEY_CURRENT_USER\Software\{UID}
{random 2 characters} = "{contents of HELP_DECRYPT.HTML}"

HKEY_CURRENT_USER\Software\{UID}
{random 2 characters} = "{contents of HELP_DECRYPT.URL}"

HKEY_CURRENT_USER\Software\{UID}\
{random key}
{Path and file of encrypted file} = "{hex values}"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\ERSvc
Start = "4"

(Note: The default value data of the said registry entry is 2.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wscsvc
Start = "4"

(Note: The default value data of the said registry entry is 2.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\BITS
Start = "4"

(Note: The default value data of the said registry entry is 2.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wuauserv
Start = "4"

(Note: The default value data of the said registry entry is 2.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SystemRestore
DisableSR = "1"

(Note: The default value data of the said registry entry is 0.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}veloper.com/tmp/b.php
  • http://{BLOCKED}la.kz/wp-content/plugins/wp-db-backup-made/a.php
  • http://{BLOCKED}h.{BLOCKED}er.com/wp-content/plugins/wp-db-backup-made/b.php
  • http://{BLOCKED}digital.com/wp-content/themes/twentytwelve/c.php
  • http://{BLOCKED}100unity.com/wp-includes/js/tinymce/skins/wordpress/images/e.php
  • http://{BLOCKED}bv.com/plugins/system/plg_system_rewrite/a.php
  • http://{BLOCKED}veloper.com/tmp/b.php
  • http://{BLOCKED}s.{BLOCKED}ngalore.org/wp-content/themes/twentyeleven/d.php
  • http://{BLOCKED}sscod.com/tmp/e.php
  • http://{BLOCKED}nadvances.com/wp-content/plugins/updraftplus/oc/guzzle/Guzzle/Service/Command/LocationVisitor/Request/a.php
  • http://{BLOCKED}rgical.com/plugins/system/plg_system_rewrite/b.php
  • http://{BLOCKED}rymexico.com/foro/vendor/symfony/http-foundation/Symfony/Component/HttpFoundation/Session/Storage/Handler/c.php
  • http://{BLOCKED}ebetterwe.com/wp-content/plugins/wp-antibot-standart/d.php
  • http://{BLOCKED}celets.ro/wp-content/themes/twentytwelve/e.php
  • http://{BLOCKED}aonline.com/plugins/system/plg_system_rewrite/a.php
  • http://{BLOCKED}el.vn/wp-content/themes/twentytwelve/b.php
  • http://{BLOCKED}yroseville.org/wp-content/plugins/wp-antibot-standart/c.php
  • http://{BLOCKED}rie.de/wp-content/plugins/revslider/css/jui/new/images/d.php
  • http://{BLOCKED}g.{BLOCKED}c.com.pk/wp-content/plugins/wp-antibot-standart/e.php
  • http://{BLOCKED}o.de/plugins/system/plg_system_rewrite/a.php
  • http://{BLOCKED}cement.com/blog/wp-content/plugins/wp-antibot-standart3/b.php
  • http://{BLOCKED}ftball.com/wp-content/themes/sports-team-theme/includes/advanced-custom-fields/assets/inc/datepicker/images/c.php
  • http://{BLOCKED}visi.info.tr/wp-content/themes/twentytwelve/d.php
  • http://{BLOCKED}k.info/wp-content/uploads/e.php
  • http://{BLOCKED}nce.ru/wp-content/themes/dreamynight-10/a.php
  • http://{BLOCKED}bahadi.com/wp-content/uploads/b.php
  • http://{BLOCKED}lemaneslabardena.com/plugins/system/plg_system_rewrite/c.php
  • http://{BLOCKED}zworld.com/wp-content/plugins/wp-antibot-standart/d.php
  • http://{BLOCKED}g.{BLOCKED}n.com.br/wp-content/plugins/wp-antibot-standart/a.php
  • http://{BLOCKED}homesearch.com/wp-content/plugins/wp-antibot-standart/b.php
  • http://{BLOCKED}ic.ro/wp-content/themes/twentytwelve/c.php
  • http://{BLOCKED}rwa.com/wp-content/plugins/wp-db-backup-made/a.php
  • http://{BLOCKED}g.{BLOCKED}c.uab.es/wordpress/wp-content/plugins/wp-db-backup-made1/d.php
  • http://{BLOCKED}lry.com/il/wp-content/plugins/ninja-forms/includes/admin/pages/ninja-forms-settings/tabs/c.php
  • http://{BLOCKED}a.com/blog/wp-content/plugins/scribe/lib/history/views/meta-box/c.php
  • http://{BLOCKED}n.ru/wp-content/plugins/nextgen-gallery/products/photocrati_nextgen/modules/nextgen_gallery_display/templates/list/a.php
  • http://{BLOCKED}n.com/wp-content/themes/twentythirteen/e.php
  • http://{BLOCKED}es.com/wp-content/themes/twentyeleven/a.php
  • http://{BLOCKED}partman.hu/de/wp-content/plugins/wp-db-backup-made/e.php
  • http://{BLOCKED}oyunlari.org/wp-content/themes/twentytwelve/b.php
  • http://{BLOCKED}magenes.com/wp-content/plugins/wp-mobile-edition/admin/includes/mobile_themes/mTheme-Unus/images/blue/a.php
  • http://{BLOCKED}ron.com/wp-content/plugins/contact-form-7/includes/js/jquery-ui/themes/smoothness/images/a.php

It deletes the initially executed copy of itself

NOTES:

It drops HELP_DECRYPT.HTML, HELP_DECRYPT.PNG, HELP_DECRYPT.TXT and HELP_DECRYPT.URL to all folders where files are encrypted.

It connects to the following non-malicious URL:

  • http://ip-addr.es
  • http://myexternalip.com/raw
  • http://curlmyip.com

  SOLUTION

Minimum Scan Engine:

9.750

Scan your computer with your Trend Micro product to delete files detected as TROJ_CRYPWALL.RUI. 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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