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Backdoor.Win32.RMSRAT.THAABCAH

November 30, 2018
 Analysis by: Warren Adam Sto. Tomas
 ALIASES:

Backdoor.Rat.Agent (Ikarus)

 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 on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites. It may be downloaded by other malware/grayware from remote sites.

  TECHNICAL DETAILS

File Size:

75,264 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

23 Nov 2018

Payload:

Drops files, Connects to URLs/IPs, Terminates processes

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.

It may be downloaded by the following malware/grayware from remote sites:

Installation

This Backdoor drops the following files:

  • %All Users Profile%\AsusGesture\settings.dat

(Note: %All Users Profile% is the common user's profile folder, which is usually C:\Documents and Settings\All Users on Windows 2000, XP, and Server 2003, or C:\ProgramData on Windows Vista, 7, and 8. )

It drops and executes the following files:

  • %User Temp%\Data1\TabSvc.exe
  • %User Temp%\exit.exe -> executes i.cmd
  • %User Temp%\i.cmd -> renames syst.dll to btc.exe
  • %User Temp%\syst.dll (renamed to btc.exe)
  • %All Users Profile%\AsusGesture\exit.exe -> executes i.cmd
  • %All Users Profile%\AsusGesture\i.cmd
  • %All Users Profile%\AsusGesture\winserv.exe -> detected as PUA.Win32.RManSys.AA

It creates the following folders:

  • %User Temp%\Data1
  • %All Users Profile%\AsusGesture

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, and 8.. %All Users Profile% is the common user's profile folder, which is usually C:\Documents and Settings\All Users on Windows 2000, XP, and Server 2003, or C:\ProgramData on Windows Vista, 7, and 8. )

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
AsusGesture = %All Users Profile%\AsusGesture\winserv.exe

Backdoor Routine

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

  • {BLOCKED}.{BLOCKED}.{BLOCKED}.16:5655

Process Termination

This Backdoor terminates the following processes if found running in the affected system's memory:

  • rundll32.exe

Other Details

This Backdoor connects to the following URL(s) to check for an Internet connection:

  • yandex.com

It does the following:

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.644.04

FIRST VSAPI PATTERN DATE:

23 Nov 2018

VSAPI OPR PATTERN File:

14.645.00

VSAPI OPR PATTERN Date:

24 Nov 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

Terminate a malware/grayware process

[ Learn More ]

*Note: If the detected process is not displayed in theWindows Task Manager, continue doing the next steps.

    • %User Temp%\exit.exe
    • %All Users Profile%\AsusGesture\exit.exe
    • %User Temp%\i.cmd
    • %All Users Profile%\AsusGesture\i.cmd
    • %All Users Profile%\AsusGesture\winserv.exe

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
    • AsusGesture = %All Users Profile%\AsusGesture\winserv.exe

Step 5

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.  
  • %User Temp%\Data1
  • %All Users Profile%\AsusGesture

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.
  • %User Temp%\Data1\TabSvc.exe
  • %User Temp%\exit.exe
  • %User Temp%\i.cmd
  • %User Temp%\syst.dll
  • %User Temp%\btc.exe
  • %All Users Profile%\AsusGesture\exit.exe
  • %All Users Profile%\AsusGesture\i.cmd
  • %All Users Profile%\AsusGesture\winserv.exe
  • %All Users Profile%\AsusGesture\settings.dat

Step 7

Scan your computer with your Trend Micro product to delete files detected as Backdoor.Win32.RMSRAT.THAABCAH. 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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