RANSOM_TBLOCKER.THBOMH

March 08, 2018
 Analysis by: Noel Anthony Llimos
 ALIASES:

Trojan.Win32.Diztakun.bgjv (KASPERSKY), Ransom:Win32/Genasom (Microsoft)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, 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 adds certain registry entries to disable the Task Manager. This action prevents users from terminating the malware process, which can usually be done via the Task Manager.

It encrypts files found in specific folders.

  TECHNICAL DETAILS

File Size:

30,208 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

13 Feb 2018

Payload:

Drops files, Disables services, 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 files:

  • %AppDataLocal%\TBlocker\{Malware File Name}.{Exe}_Url_{Random Characters}\1.0.0.0\user.config

(Note: %AppDataLocal% is the Application Data folder found in Local Settings, where it is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

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
Windows Defender = %Temp%\TBlocker.exe

Other System Modifications

This Ransomware adds the following registry entries to disable the Task Manager:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = 1

Other Details

This Ransomware does the following:

  • It executes the following commands to disable "explorer.exe":
    • "taskkill /f /im explorer.exe"
  • It displays the following lockscreen upon successful encryption of files:

Ransomware Routine

This Ransomware encrypts files found in the following folders:

  • %User Profile%\Desktop
  • %User Profile%\My Music
  • %User Profile%\My Videos
  • %User Profile%\My Pictures
  • %User Profile%\My Documents

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

It appends the following extension to the file name of the encrypted files:

  • {File Name}.{File Extension}_

NOTES:
The following key for this specific ransomware is: 580933

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

13.964.02

FIRST VSAPI PATTERN DATE:

11 Feb 2018

VSAPI OPR PATTERN File:

13.965.00

VSAPI OPR PATTERN Date:

13 Feb 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
    • Windows Defender = %Temp%\TBlocker.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies
    • SystemDisableTaskMgr = 1

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.
  • %AppDataLocal%\TBlocker\{Malware File Name}.{Exe}_Url_{Random Characters}\1.0.0.0\user.config

Step 6

Restore encrypted files from backup.

Step 7

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


Did this description help? Tell us how we did.