Ransom_MRDEC.B

August 01, 2018
 Analysis by: Noel Anthony Llimos
 ALIASES:

HEUR:Trojan.Win32.AntiAV (Kaspersky), Trojan:Win32/Tiggre!plock (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:

Dropped by other malware, 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 drops files as ransom note.

  TECHNICAL DETAILS

File Size:

13,824 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

17 Jul 2018

Payload:

Encrypts files, Displays message/message boxes

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 a copy of itself in the following folders using different file names:

  • %Windows%\searchfiles.exe

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
unlock = %System Root%\Decoding help.hta

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
searchfiles = %Windows%\searchfiles.exe

Other Details

This Ransomware does the following:

  • It displays the following dropped ransom note after restarting the system.
  • Creates a process to execute the following command to delete the shadow copy of the infected system:
    • cmd.exe /c vssadmin delete shadows /all
  • It encrypts files in fixed, removable and network drives.

Ransomware Routine

This Ransomware appends the following extension to the file name of the encrypted files:

  • [ID]16 Random Characters[ID]

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

  • {Encrypted Directory}\Decoding help.hta

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.384.04

FIRST VSAPI PATTERN DATE:

17 Jul 2018

VSAPI OPR PATTERN File:

14.385.00

VSAPI OPR PATTERN Date:

18 Jul 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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • unlock = %System Root%\Decoding help.hta
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • searchfiles = %Windows%\searchfiles.exe

Step 5

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.
  • %Windows%\searchfiles.exe
  • {Encrypted Directory}\Decoding help.hta

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom_MRDEC.B. 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.


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