Analysis by: Michael Jhon Ofiaza
ALIASES:

Trojan-Ransom.Win32.Encoder.n (Kaspersky) ; Trojan:Win32/Skeeyah.A!rfn (Microsoft)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet

This Ransomware arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It connects to certain websites to send and receive information. However, as of this writing, the said sites are inaccessible. It deletes itself after execution.

It drops files as ransom note.

  TECHNICAL DETAILS

File Size: 2,958,848 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 09 Aug 2018
Payload: Connects to URLs/IPs, Displays message/message boxes, Encrypts files

Arrival Details

This Ransomware 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 Ransomware drops the following copies of itself into the affected system and executes them:

  • %AppDataLocal%\{Malware Name}.exe

(Note: %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista, 7, and 8.)

It drops the following files:

  • %User Temp%\delself.bat -> used to delete the malware copy and itself

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, and 8.)

It adds the following processes:

  • %AppDataLocal%\{Malware Name}.exe
  • %User Temp%\delself.bat
  • %AppDataLocal%\{Malware Name}.exe --Admin
  • %AppDataLocal%\{Malware Name}.exe" --ForNetRes x5I74v4h003xJ0iyhUfHQ8W6o0RDSicmSfg72KVA 6se9RaIxXF9m70zWmx7nL3bVRp691w4SNY8UCir0
  • %AppDataLocal%\{Malware Name}.exe" --Service {Random Hex} x5I74v4h003xJ0iyhUfHQ8W6o0RDSicmSfg72KVA 6se9RaIxXF9m70zWmx7nL3bVRp691w4SNY8UCir0
  • %AppDataLocal%\{Malware Name}.exe" --Service {Random Hex} x5I74v4h003xJ0iyhUfHQ8W6o0RDSicmSfg72KVA 6se9RaIxXF9m70zWmx7nL3bVRp691w4SNY8UCir0

(Note: %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista, 7, and 8.. %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, and 8.)

Autostart Technique

This Ransomware adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
SysHelper = %AppDataLocal%\{Malware Name}.exe --AutoStart x5I74v4h003xJ0iyhUfHQ8W6o0RDSicmSfg72KVA 6se9RaIxXF9m70zWmx7nL3bVRp691w4SNY8UCir0

Other Details

This Ransomware connects to the following website to send and receive information:

  • cosonar.{BLOCKED}r.ru/get.php

It does the following:

  • Have a hidden form that can be display by pressing ALT+F8
  • The Attacker can customize the following data:
    • Key
    • Filename of Ransom Note
    • Content of Ransom Note
    • Personal ID
    • Extension to be appended on the encrypted files
    • List of paths that will not be encrypted

However, as of this writing, the said sites are inaccessible.

It deletes itself after execution.

Ransomware Routine

This Ransomware avoids encrypting files found in the following folders:

  • C:\Windows\
  • C:\Program Files (x86)\Mozilla Firefox\
  • C:\Program Files (x86)\Internet Explorer\
  • C:\Program Files (x86)\Google\
  • C:\Program Files\Mozilla Firefox\
  • C:\Program Files\Internet Explorer\
  • C:\Program Files\Google\
  • D:\Windows\
  • D:\Program Files (x86)\Mozilla Firefox\
  • D:\Program Files (x86)\Internet Explorer\
  • D:\Program Files (x86)\Google\
  • D:\Program Files\Mozilla Firefox\
  • D:\Program Files\Internet Explorer\
  • D:\Program Files\Google\

It drops the following file(s) as ransom note:

  • {Encrypted Folder}\!!!KEYPASS_DECRYPTION_INFO!!!.txt

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 14.442.02
FIRST VSAPI PATTERN DATE: 14 Aug 2018
VSAPI OPR PATTERN File: 14.443.00
VSAPI OPR PATTERN Date: 15 Aug 2018

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • SysHelper = %AppDataLocal%\{Malware Name}.exe --AutoStart x5I74v4h003xJ0iyhUfHQ8W6o0RDSicmSfg72KVA 6se9RaIxXF9m70zWmx7nL3bVRp691w4SNY8UCir0

Step 5

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • {Encrypted Folder}\!!!KEYPASS_DECRYPTION_INFO!!!.txt
  • %User Temp%\delself.bat
  • %AppDataLocal%\{Malware Name}.exe

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as RANSOM_ENCODER.THHADAH. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.

Step 7

Restore encrypted files from backup.

Step 8

Scan your computer with your Trend Micro product to delete files detected as RANSOM_ENCODER.THHADAH. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check the following Trend Micro Support pages for more information:


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