Analysis by: Francis Xavier Antazo
ALIASES:

Ransom:Win32/Tescrypt (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. It is capable of encrypting files in the affected system.

  TECHNICAL DETAILS

File Size: 384512 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 23 Feb 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 and executes them:

  • %Windows%\{random filename}.exe

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

It drops the following files:

  • %User Profile%\Documents\recover_file_{random letters}.txt
  • %Desktop%\RECOVERY.HTM
  • %Desktop%\RECOVERY.png
  • %Desktop%\RECOVERY.TXT
  • {Folders containg encrypted files}\Recovery+{random letters}.png
  • {Folders containg encrypted files}\Recovery+{random letters}.txt
  • {Folders containg encrypted files}\Recovery+{random letters}.html

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %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.)

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} = "%System%\cmd.exe /c start "" "%Windows%\{random filename}.exe""

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\xxxsys

HKEY_CURRENT_USER\Software\{Installation ID}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\{Installation ID}
data = {encryption information}

HKEY_CURRENT_USER\Software\xxxsys
ID = {Installation ID}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
EnabledLinkConnections = "1"

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://www.{BLOCKED}la.com/imgs/videos/bsts.php
  • http://{BLOCKED}e.co.kr/board/common/bsts.php
  • http://{BLOCKED}e.co.kr/board/common/bsts.php
  • http://{BLOCKED}i.com/whiteboard_dangam/admin/bsts.php
  • http://{BLOCKED}inslow.com/csys.php
  • http://{BLOCKED}dress.pl/wp-content/themes/sketch/csys.php

It deletes the initially executed copy of itself

It is capable of encrypting files in the affected system.

NOTES:

It appends the extension .mp3 to the file name of the encrypted files.