Analysis by: Carl Maverick Pascual

ALIASES:

Trojan:Win32/Gandcrab.AF (Microsoft) ; W32/GandCrab.B!tr (Fortinet)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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 encrypts files found in specific folders.

  TECHNICAL DETAILS

File Size: 171,008 bytes
Memory Resident: No
Initial Samples Received Date: 16 Aug 2018

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 files:

  • {Encrypted Directory}:\_HELP_INSTRUCTION.TXT

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

  • %ProgramData%\{10 Random Values}.exe

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This contains application data for all users. This is usually C:\ProgramData in 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
{10 Random Characters} = "{Malware directory}\{Malware File Name}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{10 Random Characters} = "%ProgramData%\{10 Random Hex Values}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
*{10 Random Characters} = "%ProgramData%\{10 Random Hex Values}.exe"

Other System Modifications

This Ransomware adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion
{8 Random Characters} = {Number of encrypted files}

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion
{10 Random Characters} = {Random Values}

Other Details

This Ransomware does the following:

  • After the file-encryption process, it executes the ransom note _HELP_INSTRUCTION.txt using notepad:

Ransomware Routine

This Ransomware encrypts files found in the following folders:

  • {Fixed Drive}
  • {Removable Drive}
  • {Network Drive}

It avoids encrypting files with the following strings in their file name:

  • bootmgr
  • ntldr
  • NTLDR
  • NTDETECT.COM
  • ntdetect.com

It avoids encrypting files found in the following folders:

  • %Windows%
  • %ProgramData%
  • %Program Files%

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.. %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This contains application data for all users. This is usually C:\ProgramData in Windows Vista, 7, and 8.. %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000, Server 2003, and XP (32-bit), Vista (32-bit), 7 (32-bit), and 8 (32-bit), or C:\Program Files (x86) in Windows XP (64-bit), Vista (64-bit), 7 (64-bit), and 8 (64-bit).)

It renames encrypted files using the following names:

  • {32 Random Characters}.SYS

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 14.448.02
FIRST VSAPI PATTERN DATE: 17 Aug 2018
VSAPI OPR PATTERN File: 14.449.00
VSAPI OPR PATTERN Date: 18 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

Identify and terminate files detected as RANSOM_CRYPTOMIX.J

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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
    • {10 Random Hex Values} = "{Malware directory}\{Malware File Name}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {10 Random Hex Values} = "C:\ProgramData\{10 Random Hex Values}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce
    • *{10 Random Hex Values} = "C:\ProgramData\{10 Random Hex Values}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion
    • {8 Random Hex Values} = {Number of encrypted files}
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion
    • {10 Random Hex Values} = {Decryption Key}

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.
  • %ProgramData%\{10 Random Characters}.exe

Step 6

Restore encrypted files from backup.

Step 7

Scan your computer with your Trend Micro product to delete files detected as RANSOM_CRYPTOMIX.J. 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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