Analysis by: Francis Xavier Antazo
ALIASES:

Ransom:Win32/Crowti (Microsoft); Trojan-Ransom.Win32.Cryptodef.yon (Kaspersky);

 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: 200704 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 08 Sep 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}publications.com/wp-includes/theme-compat/ap1.php
  • {BLOCKEDvac.ca/ap1.php
  • {BLOCKEDu-kanban.net/wordpress/wp-content/plugins/akismet/_inc/img/ap2.php
  • {BLOCKEDhosp.com/hagg2013/wp-includes/theme-compat/ap3.php
  • {BLOCKEDtion.com/ap4.php
  • {BLOCKED}vap.com/mtqzpa/templates/ap5.php
  • {BLOCKED}ttec.com/assets/fonts/ap1.php
  • {BLOCKED}ttec.com/assets/fonts/ap1.php
  • {BLOCKED}oparquettes.com/wp-content/uploads/2014/07/ap3.php
  • {BLOCKED}ainjurycenters.com/backups_georgia/back%2007102014/ap4.php
  • {BLOCKED}l.com.ng/js/vendor/ap5.php
  • {BLOCKED}ercables.com/wp-admin/user/ap1.php
  • {BLOCKED}uty.net/wp-includes/certificates/ap2.php
  • {BLOCKED}a.net/wp-admin/js/ap3.php
  • {BLOCKED}ritysystems.com/js/ap4.php
  • {BLOCKED}mission.org/wp-includes/theme-compat/ap5.php
  • {BLOCKED}lyclinic.com/gallery/small/ap1.php
  • {BLOCKED}urityservices.com/wp-admin/images/ap2.php
  • {BLOCKED}somaha.net/wp-includes/Text/Diff/Renderer/ap3.php
  • {BLOCKED}teabouteverything.com/wp-includes/pomo/ap4.php
  • {BLOCKED}esolutions.co.in/wp-content/plugins/tinymce-advanced/css/ap5.php
  • {BLOCKED}nebleau-miami.com/ap1.php
  • {BLOCKED}ioneciampi.org/nuovo/blogs/media/ap2.php
  • {BLOCKED}usicktv.com/ap3.php
  • {BLOCKED}n.com/wp-admin/maint/ap4.php
  • {BLOCKED}t.com/wp-includes/fonts/ap5.php
  • {BLOCKED}chmifty.com/ap1.php
  • {BLOCKED}ilver.com/controller/catalog/ap2.php
  • {BLOCKED}cepts.net/wp-content/plugins/indonez-shortcodes/js/ap3.php
  • {BLOCKED}albatterycase.com/wp-admin/js/ap4.php
  • {BLOCKED}o.com/wp-admin/network/ap5.php
  • {BLOCKED}ngcareers.co.uk/images/prettyPhoto/light_square/ap1.php
  • {BLOCKED}e-academy.net/wp-admin/user/ap2.php
  • {BLOCKED}obonato.com/wp-content/uploads/js_composer/ap3.php
  • {BLOCKED}pro.com/css/fonts/ap4.php
  • {BLOCKED}ub.org/css/fonts/ap5.php
  • {BLOCKED}atee.com/wp-includes/css/ap1.php
  • {BLOCKED}ernet.com/ap2.php
  • {BLOCKED}aerengwa.com/user/most-instagram-followers-non-celebrity/ap3.php
  • {BLOCKED}al.co.uk/js-js/ap4.php
  • {BLOCKED}lex.com/ndst.ng/wp-admin/images/ap5.php
  • {BLOCKED}ook.com/bat/ap1.php
  • {BLOCKED}nce.com/wp-includes/theme-compat/ap2.php
  • {BLOCKED}itnessproduct.com/wp-admin/js/ap3.php
  • {BLOCKED}reencondo.com/wp-content/cache/ap4.php
  • {BLOCKED}verpartners.org/wp-includes/theme-compat/ap5.php
  • {BLOCKED}ublications.com/wp-includes/theme-compat/ap1.php
  • {BLOCKED}muadong.com/wp-includes/fonts/ap2.php
  • {BLOCKED}atsmiles.com/old/wp-includes/theme-compat/ap3.php
  • {BLOCKED}so.com/mtqzpa/templates/ap4.php
  • {BLOCKED}ccafountain.com/Saffron/wp-content/themes/medica-lite/ap5.php
  • {BLOCKED}nijn.com/wp-includes/theme-compat/ap1.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.