RANSOM_CRYPWALL.YUYAHC

January 14, 2016
 Analysis by: Jeanne Jocson
 ALIASES:

Ransom:Win32/Crowti.A(Microsoft),Win32/Filecoder.FJ trojan(ESET-NOD32),Trojan-Ransom.Win32.Cryptodef.acgv(Kaspersky)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE 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. It is capable of encrypting files in the affected system.

  TECHNICAL DETAILS

File Size:

335872 bytes

File Type:

EXE

Initial Samples Received Date:

13 Jan 2016

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:

  • %Application Data%\{random 8 characters}\{random 7 characters}.exe

(Note: %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.)

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}\{random 7 characters}.exe"

Dropping Routine

This Trojan drops the following files:

  • {directory of encrypted file}\HELP_YOUR_FILES.PNG

Other Details

This Trojan deletes itself after execution.

It is capable of encrypting files in the affected system.