RANSOM_CRYPTESLA.YUYAKF

May 10, 2016
 Analysis by: Rhena Inocencio
 ALIASES:

Ransom:Win32/Tescrypt!rfn (Microsoft), Ransomware-FEJ!8163ED7BBFA6 (McAfee)

 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:

Varies

File Type:

EXE

Initial Samples Received Date:

29 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 files:

  • %My Documents%\+recover+file.txt
  • %Desktop%\+REcovER+{random}.TXT
  • %Desktop%\+REcovER+{random}.PNG
  • {folders containing encrypted files}\+REcovER+{random}.png
  • {folders containing encrypted files}\+REcovER+{random}.txt

(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.)

It drops the following copies of itself into the affected system:

  • %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.)

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 characters} = "C:\WINDOWS\SYSTEM32\CMD.EXE /C START "" "%My Documents%\{random filename}.exe""

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\Axronics

HKEY_CURRENT_USER\Software\{ID}

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
EnableLinkedConnections = "1"

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}benovitz.com/qhcka/templates/binarystings.php
  • http://{BLOCKED}kecantikan.com/wp-content/plugins/contact-form-7/includes/js/jquery-ui/themes/smoothness/images/binarystings.php
  • http://{BLOCKED}u.org/wp-content/plugins/profile-builder/assets/lib/wck-api/assets/js/tiny_mce/utils/binarystings.php
  • http://{BLOCKED}it.in/wp-content/plugins/wpclef/assets/src/sass/neat/grid/binarystings.php
  • http://{BLOCKED}ftheworld.org/cgi-bin/binarystings.php
  • http://{BLOCKED}0.com/wp-content/themes/vtc360_maxf3d/ReduxFramework/ReduxCore/inc/extensions/wbc_importer/demo-data/Demo2/binarystings.php

It does the following:

  • It encrypts files in all fixed, removable, and network drives and shares.

It deletes the initially executed copy of itself