Analysis by: Michael Jay Villanueva

 ALIASES:

Trojan:Win32/Dynamer!ac (Microsoft); Ransom.KozyJozy (Malwarebytes); Trojan-Ransom.MSIL.Geograph.r (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

This ransomware has the ability to encrypt files found on an affected system. This routine makes these files inaccessible until a ransom is paid. Should the user not pay the ransom, the encrypted files will remain unusable. It is detected to use RSA 2048 asymmetric encryption to encrypt said files, making it impossible for the files to be decrypted without paying the ransom.

To get a one-glance comprehensive view of the behavior of this Trojan, refer to the Threat Diagram shown below.

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: 143,872 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 21 Jun 2016
Payload: Drops files, Encrypts files

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 component file(s):

  • %User Profile%\w.jpg - ransom note

Other System Modifications

This Trojan adds the following registry entries:

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
wall = %User Profile%\w.jpg

Other Details

This Trojan encrypts files with the following extensions:

  • .1cd
  • .7z
  • .accdb
  • .arj
  • .bmp
  • .cd
  • .cdr
  • .dbf
  • .doc
  • .docx
  • .epf
  • .jpeg
  • .jpg
  • .ldf
  • .max
  • .md
  • .mdb
  • .mdf
  • .odb
  • .odg
  • .ods
  • .odt
  • .pdf
  • .png
  • .ppt
  • .pptx
  • .psd
  • .rar
  • .rtf
  • .tar
  • .tif
  • .xls
  • .xlsx
  • .zip

It renames encrypted files using the following names:

  • {Original Filename}.31392E30362E32303136_{Key_ID}_LSBJ1

It does the following:

  • It deletes shadow copies by executing the following command:
    • vssadmin.exe Delete Shadows /All /Quiet

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 12.604.08
FIRST VSAPI PATTERN DATE: 21 Jun 2016
VSAPI OPR PATTERN File: 12.605.00
VSAPI OPR PATTERN Date: 22 Jun 2016

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

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
    • wall = %User Profile%\w.jpg

Step 4

Search and delete these files

[ 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.
  • %User Profile%\w.jpg

Step 5

Scan your computer with your Trend Micro product to delete files detected as RANSOM_JOKOZY.A. 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 6

Restore encrypted files from backup.


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