Analysis by: David John Agni
ALIASES:

Ransom:Win32/Crowti.A (Microsoft)

 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: 245,760 bytes
Memory Resident: Yes
Initial Samples Received Date: 20 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 8 Characters}\{Random 8 Characters}.exe
  • %Application Data%\{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.)

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:

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

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
*{Second to the Sixth Characters {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
*{Last Seven Characters of {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:

HKEY_CURRENT_USER\Software
Local AppWizard-Generated Applications =

HKEY_CURRENT_USER\Software\Local AppWizard-Generated Applications
WebBrowse =

HKEY_CURRENT_USER\Software\Local AppWizard-Generated Applications\
WebBrowse
Recent File List =

HKEY_CURRENT_USER\Software\Local AppWizard-Generated Applications\
WebBrowse
Settings =

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}a87.com/img2.php?{Random Letter}={Random Value}
  • http://{BLOCKED}r.com/img4.php?{Random Letter}={Random Value}
  • http://{BLOCKED}s.org/img4.php?{Random Letter}={Random Value}

It deletes the initially executed copy of itself

NOTES:

This Trojan encrypts files with certain extensions in the affected system hard drive. It drops the files HELP_DECRYPT.HTML, HELP_DECRYPT.PNG, HELP_DECRYPT.TXT, and HELP_DECRYPT.URL to all folders where files are encrypted.