Analysis by: Michael Jay Villanueva

ALIASES:

TrojanDropper:Win32/Etumbot.A!dha (Microsoft)

 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: Downloaded from the Internet, Dropped by other malware

This Backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It does not have any propagation routine.

It executes commands from a remote malicious user, effectively compromising the affected system. However, as of this writing, the said sites are inaccessible.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 105,472 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 30 Aug 2017
Payload: Connects to URLs/IPs, Drops files, Compromises system security

Arrival Details

This Backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

It 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 adds the following folders:

  • %Application Data%\LHA

(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 drops the following files:

  • {Current Malware Path}\~bctp2a -> encrypted form of the fake document, deleted afterwards

It drops and executes the following files:

  • {Full malware path and filename excluding the extension, minus 4 characters at the end}.doc -> decrypted form of fake document, executed by the malware in order to distract the user while the main malicious routine (backdoor) is afftecting the system
    For example:
    C:\Test\1.exe -> C:\Te.doc
  • %Application Data%\LHA\LHAUpd.exe -> detected as BKDR_ETUMBOT.NUO

(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.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
LHAUpd = "%AppData%\LHA\LHAUpd.exe"

Propagation

This Backdoor does not have any propagation routine.

Backdoor Routine

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

  • Execute arbitrary files/codes
  • Download files
  • Upload files
  • Delete files
  • Enumerate printers
  • Sleep

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

  • http://{BLOCKED}.{BLOCKED}.115.83/library/ja-jp/{ID}={Generated Infected Computer’s ID with an appended random numbers}/ta=3afe27aa-6c2d-5c21-94de-8bc342ec72b2/bm={random code number}#{Encrypted Data}
    where {Encrypted Data} contains the encrypted form of the gathered information from the affected machine

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

Information Theft

This Backdoor gathers the following data:

  • User Name
  • Computer Name
  • IP Address
  • OS Version
  • System Directory

Other Details

This Backdoor deletes itself after execution.

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 13.632.06
FIRST VSAPI PATTERN DATE: 01 Sep 2017
VSAPI OPR PATTERN File: 13.633.00
VSAPI OPR PATTERN Date: 02 Sep 2017

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

Identify and terminate files detected as BKDR_ETUMBOT.NUO

[ 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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • LHAUpd = %AppData%\LHA\LHAUpd.exe

Step 6

Search and delete this folder

[ 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.
  • %Application Data%\LHA

Step 7

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.
  • {Current Malware Path}\~bctp2a
  • {Full malware path and filename excluding the extension, minus 4 characters at the end}.doc
  • %Application Data%\LHA\LHAUpd.exe

Step 8

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


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