Analysis by: Noel Anthony Llimos
ALIASES:

HEUR:Trojan.Win32.Agent.gen (Kaspersky), W32.Rontokbro@mm (Norton)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Dropped by other malware

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.

  TECHNICAL DETAILS

File Size: 551,936 bytes
File Type: EXE
File Compression: Delphi
Memory Resident: Yes
Initial Samples Received Date: 05 Jun 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 the following copies of itself into the affected system:

  • %Windows%\ScreenSaver.scr

(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_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
SCRService = %Windows%\ScreenSaver.scr

Download Routine

This Ransomware connects to the following URL(s) to download its configuration file:

  • http://{BLOCKED}web.cf/aes.js → Javascript implementation of AES encryption

Other Details

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

  • http://{BLOCKED}web.cf/

It does the following:

  • It disables the execution of the following applications by adding the following registry entries:
    • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\{application}
      • Debugger = "%Windows%\ScreenSaver.scr"

    Where {application} can be any of the following:
    • explorer.exe
    • tor.exe
    • chrome.exe
    • svchost.exe
    • opera.exe
    • iexplore.exe
    • firefox.exe
    • WinRAR.exe
    • mbam.exe
    • skype.exe
    • Microsoft.Photos.exe
    • mspaint.exe
    • SearchIndexer.exe
    • rstrui.exe
    • setup.exe
    • safari.exe
    • MicrosoftEdge.exe
    • SystemSettings.exe
    • taskmgr.exe
    • plugin-container.exe
    • dwm.exe
    • conhost.exe
    • updater.exe
    • regedit.exe
    • rundll32.exe
    • cmd.exe
    • avast.exe
  • Clicking the exit button on its UI will shutdown the system by executing the following command:
    • shutdown -s -t 4
  • It displays the following UI as its ransom note:
  • This ransomware does not encrypt files.

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

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 14.296.01
FIRST VSAPI PATTERN DATE: 05 Jun 2018
VSAPI OPR PATTERN File: 14.297.00
VSAPI OPR PATTERN Date: 06 Jun 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 key

[ 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 NT\CurrentVersion\Image File Execution Options\{application}
    • Debugger = "%Windows%\ScreenSaver.scr"

Step 5

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
    • SCRService = %Windows%\ScreenSaver.scr

Step 6

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.
  • %Windows%\ScreenSaver.scr

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as RANSOM_PEDCOT.THFOEAH. 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 8

Restore encrypted files from backup.

Step 9

Scan your computer with your Trend Micro product to delete files detected as RANSOM_PEDCOT.THFOEAH. 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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