Analysis by: Patrick Angelo Roderno
ALIASES:

Trojan:Win32/Dynamer!rfn (MICROSOFT); Gen:Variant.Strictor.158619 (BITDEFENDER); RDN/Generic.grp (NAI)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

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

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size: 846,336 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 09 Feb 2018
Payload: Compromises system security, Connects to URLs/IPs, Steals information

Arrival Details

This Backdoor 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 Backdoor drops the following copies of itself into the affected system and executes them:

  • %Application Data%\Brix\brix.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • eohSEArfS1nJ0SBOsCLroQ1B1nYZnEjM

Backdoor Routine

This Backdoor opens the following port(s) where it listens for remote commands:

  • 23558

It executes the following commands from a remote malicious user:

  • Initialize itself in the affected system
  • Download and execute files
  • Upload and execute files
  • Uninstall itself
  • Screen management
  • Get all running processes
  • Terminate specified processes
  • Start a specified process
  • Get all logical drives of the affected system
  • Get all files in a specified directory
  • Download arbitrary files
  • Perform mouse clicks
  • Get system information such as username, PC name, MAC address, etc.
  • Firewall detection
  • Visit a website
  • Display message boxes
  • Update arbitrary files
  • Perform shell commands
  • Rename files
  • Delete files
  • Can shutdown, restart, or suspend the affected system
  • Get all startup items
  • Add a startup item
  • Stop a file from being downloaded

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • {BLOCKED}os.com

Information Theft

This Backdoor gathers the following data:

  • Operating System
  • Account type of current user
  • Geographical location of the affected system (using "freegeoip.net")

Other Details

This Backdoor does the following:

  • If the user has administrator privileges, it creates the following registry entries to enable its automatic execution at every system startup:
    • HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Run
      Brix = %Application Data%\Brix\brix.exe
    • HKEY_CURRENT_USER/Software/Microsoft/Windows/CurrentVersion/Run
      Brix = %Application Data%\Brix\brix.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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.)

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 14.166.03
FIRST VSAPI PATTERN DATE: 02 Apr 2018
VSAPI OPR PATTERN File: 14.167.00
VSAPI OPR PATTERN Date: 03 Apr 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 BKDR_XRAT.KVL

[ 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_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • Brix = %Application Data%\Brix\brix.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Brix = %Application Data%\Brix\brix.exe

Step 5

Scan your computer with your Trend Micro product to delete files detected as BKDR_XRAT.KVL. 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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