Analysis by: Patrick Noel Collado
ALIASES:

Trojan:Win32/Milum!MS (Microsoft), Backdoor.Win32.Agent.mytpug (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • 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: 520,704 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 12 Apr 2020
Payload: Connects to URLs/IPs

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 files:

  • %ProgramData%\Micapp\Windows\cnf.dat

(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 on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

It drops and executes the following files:

  • %ProgramData%\Micapp\Windows\{Malware name}.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 on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

It adds the following processes:

  • %System32%\cmd.exe /c FOR /l %i in (1,1,10) DO IF NOT EXIST "{Malware Path}\{Malware Name}" (start "" "%ProgramData%\Micapp\Windows\{Malware Name}" & exit) ELSE ((DEL /F /Q "{Malware Path}\{Malware Name}") & timeout /t 1)
  • %System32%\cmd.exe timeout /t 1
  • %ProgramData%\Micapp\Windows\{Malware name}.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 on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

It creates the following folders:

  • %ProgramData%\Micapp\Windows

(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 on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

Autostart Technique

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

HKEY_USERS\{USER SID}\Software\
Microsoft\Windows\CurrentVersion\
Run
CstartHelper = %ProgramData%\Micapp\Windows\{Malware Name}.exe

Backdoor Routine

This Backdoor executes the following commands from a remote malicious user:

  • Execute commands and return result through pipe
  • Decode received content then drop to file in path field
  • Encode file in path field then send
  • Get file info
  • Uninstall (run batch script to delete itself)
  • Get command execution result
  • Get system information (Windows version, CPU architecture, host name, username, AV Products)
  • Get directory info
  • Update malware (download new version and remove old one)

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

  • www.{BLOCKED}versys1212.com/rl.php
  • {BLOCKED}.{BLOCKED}.3.86/page/view.php
  • {BLOCKED}.{BLOCKED}.87.172/page/view.php

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 15.804.07
FIRST VSAPI PATTERN DATE: 14 Apr 2020
VSAPI OPR PATTERN File: 15.805.00
VSAPI OPR PATTERN Date: 15 Apr 2020

Step 1

Trend Micro Predictive Machine Learning detects and blocks malware at the first sign of its existence, before it executes on your system. When enabled, your Trend Micro product detects this malware under the following machine learning name:

    Troj.Win32.TRX.XXPE50FFF0

Step 2

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 users must disable System Restore to allow full scanning of their computers.

Step 3

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 4

Identify and terminate files detected as Backdoor.Win32.MILUM.A

[ 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 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_USERS\{USER SID}\Software\Microsoft\Windows\CurrentVersion\Run
    • CstartHelper = %ProgramData%\Micapp\Windows\{Malware Name}.exe

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.
  • %ProgramData%\Micapp\Windows\cnf.dat
  • %ProgramData%\Micapp\Windows\{Malware name}.exe

Step 7

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %ProgramData%\Micapp\Windows\

Step 8

Scan your computer with your Trend Micro product to delete files detected as Backdoor.Win32.MILUM.A. 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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