Analysis by: Robert Nicole Malagad
 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. However, as of this writing, the said sites are inaccessible.

It gathers information and reports it to its servers.

  TECHNICAL DETAILS

File Size: 667,648 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 28 Feb 2018
Payload: Connects to URLs/IPs, Steals information, Compromises system security

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 file(s)/component(s):

  • %Application Data%\remcos\logs.dat ← component file
  • %User Temp%\Install.vbs ← used for decryption and installation. deleted afterwards

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, and 8.. %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.)

It drops and executes the following files:

  • %Application Data%/remcos/remcos.exe

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, and 8.)

It creates the following folders:

  • %Application Data%\remcos

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, and 8.)

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

  • Remcos_Mutex_Inj

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
remcos = %Application Data%/remcos/remcos.exe

Other System Modifications

This Backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\{random characters}-{random characters}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\{random characters}-{random characters}
exepath = {hex values}

Backdoor Routine

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

  • Perform ping
  • Enumerate drives
  • List all files
  • Open file/s
  • Get file/s from affected computer
  • Upload file/s to affected computer
  • Delete file/s from affected computer
  • Rename file/s from affected computer
  • Create new directory
  • Search a file from affected computer
  • Download file from url
  • Download file from local
  • Enumerate process
  • Terminate process
  • Maximize/Minimize application
  • Switch application
  • Terminate application
  • Open cmd
  • Open webpage
  • Open screen capture
  • Open keylogger
  • Set affected computer to send logs automatically
  • Deletes cookies and stored browser logins
  • Get screenshot
  • Capture image from camera if available
  • Acquire user password
  • Display a messagebox to affected computer
  • Sends keyboard input
  • Sends mouse click
  • Shutdown affected Computer
  • Copy clipboard data
  • Set clipboard data
  • Clear clipboard data
  • Manipulate registry entries

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

  • {BLOCKED}attaa4111.{BLOCKED}tp.com

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

Other Details

This Backdoor gathers the following information and reports it to its servers:

  • Computer Name
  • System Type
  • Product Name
  • Primary Adapter
  • User Access (Admin or Non-admin)
  • User Profile
  • User Name
  • User Domain
  • Processor Revision No.
  • Processor Level
  • Processor Identifier
  • Processor Architecture
  • System Type (32-bit or 64-bit)

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 14.102.02
FIRST VSAPI PATTERN DATE: 01 Mar 2018
VSAPI OPR PATTERN File: 14.103.00
VSAPI OPR PATTERN Date: 02 Mar 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 key

[ 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
    • remcos = %Application Data%/remcos/remcos.exe
  • In HKEY_CURRENT_USER\Software\{random characters}-{random characters}
    • EXEpath = {Hex}

Step 5

Identify and terminate files detected as BKDR_RESCOMS.YYWN

[ 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 6

Search and delete these files

[ 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.
  • %Application Data%\remcos\remcos.exe
  • %Application Data%\remcos\logs.dat
  • %User Temp%\Install.vbs

Step 7

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%\Remcos

Step 8

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