RANSOM_CRYPTESLA.YUYAKA

March 25, 2016
 Analysis by: Rhena Inocencio
 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.

  TECHNICAL DETAILS

File Size:

360,448 bytes

File Type:

EXE

Initial Samples Received Date:

24 Mar 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:

  • %My Documents%\{random filename}.exe

    (Note: %My Documents% is usually C:\Documents and Settings\{user name}\My Documents on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\Documents on Windows Vista and 7.)

It drops the following file(s)/component(s):

  • {folders containing encrypted files}\+-xxx-HELP-xxx-+{random characters}-+.png
  • {folders containing encrypted files}\+-xxx-HELP-xxx-+{random characters}-+.txt
  • {folders containing encrypted files}\+-xxx-HELP-xxx-+{random characters}-+.html
  • %Desktop%\+-xxx-HELP-xxx-+{random characters}-+.png
  • %Desktop%\+-xxx-HELP-xxx-+{random characters}-+.txt
  • %Desktop%\+-xxx-HELP-xxx-+{random characters}-+.html
  • %My Documents%\-HELP-file.txt

    (Note: %My Documents% is usually C:\Documents and Settings\{user name}\My Documents on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\Documents on Windows Vista and 7.)

(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.)

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
svc-{random characters} = "%System%\cmd /C start "" "%My Documents%\{random filename}.exe""

Other System Modifications

This Trojan adds the following registry entries:

HKEY_CURRENT_USER\Software\trueimg
ID = "{ID}"

HKEY_CURRENT_USER\Software\{ID}
data = "{random values}"

It adds the following registry keys as part of its installation routine:

HKEY_CURRENT_USER\Software\trueimg

HKEY_CURRENT_USER\Software\{ID}

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}2k15.in/sysstr.php
  • http://{BLOCKED}y.org/sysstr.php
  • http://{BLOCKED}l.com/sysstr.php
  • http://{BLOCKED}sports.info/sysstr.php
  • http://{BLOCKED}legue.com/sysstr.php
  • http://{BLOCKED}ia.com/sysstr.php

It does the following:

  • It encrypts files
  • It does not append extension to encrypted files