Trojan.Win32.BLUEROH.RPA

April 23, 2019
 Analysis by: Patrick Angelo Roderno
 ALIASES:

Trojan.Win32.Siscos.wgv (KASPERSKY); A Variant Of Win32/Kryptik.FHSF (ESET-NOD32); Backdoor:Win32/Zegost!rfn (MICROSOFT)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware

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

  TECHNICAL DETAILS

File Size:

92,160 bytes

File Compression:

UPX

Memory Resident:

No

Initial Samples Received Date:

09 Mar 2019

Payload:

Connects to URLs/IPs, Drops files

Arrival Details

This Trojan 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 Trojan drops a copy of itself in the following folders using different file names:

  • %User Temp%\{random numbers}\TemporaryFile\TemporaryFile

(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.)

It drops and executes the following files:

  • %User Temp%\nmbsawer.exe
  • %System%\{random 6-character string}.exe

(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.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It creates the following folders:

  • %User Temp%\{random numbers}\TemporaryFile

(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.)

Autostart Technique

This Trojan adds and runs the following services:

  • Service name: nprrstu
    Display name: nprrstu Wxyabcde Ghijklmn Pqrs
    Description: nprrstu Yabcdefgh Jklmnop Rstuvwxy Bcd
    Path to executable: %System%\{random 6-character string}.exe
    Startup type: Automatic

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

Download Routine

This Trojan connects to the following website(s) to download and execute a malicious file:

  • http://fid.{BLOCKED}b.se/wercplhost.exe

It saves the files it downloads using the following names:

Other Details

This Trojan does the following:

  • The dropped malware %User Temp%\nmbsawer.exe moves and renames itself to %System%\{random numbers}.bak

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.946.07

FIRST VSAPI PATTERN DATE:

18 Apr 2019

VSAPI OPR PATTERN File:

14.947.00

VSAPI OPR PATTERN Date:

19 Apr 2019

Step 1

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 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

Disable this malware service

[ Learn More ]
  • nprrstu

Step 5

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.
  • %User Temp%\{random numbers}\TemporaryFile

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.
  • %User Temp%\nmbsawer.exe
  • %User Temp%\wercplhost.exe
  • %System%\{random 6-character string}.exe
  • %System%\{random numbers}.bak

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Trojan.Win32.BLUEROH.RPA. 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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