Analysis by: Cris Nowell Pantanilla

ALIASES:

VirTool:VBS/Obfuscator.TO (Microsoft), VBS.Dunihi (Symantec), VBS/Dinihou-A (Sophos)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 REPORTED INFECTION:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This backdoor arrives via removable drives. 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 drops copies of itself in all removable drives.

It runs certain commands that it receives remotely from a malicious user. Doing this puts the affected computer and information found on the computer at greater risk.

  TECHNICAL DETAILS

File Size: 217,269 bytes
File Type: VBS
Memory Resident: Yes
Initial Samples Received Date: 07 Dec 2016

Arrival Details

This backdoor arrives via removable drives.

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 drops the following copies of itself into the affected system:

  • %User Temp%\{malware filename}.vbs

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp 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.)

Propagation

This backdoor drops copies of itself in all removable drives.

Backdoor Routine

This backdoor executes the following command(s) from a remote malicious user:

  • execute ← Execute File
  • update ← Update self
  • uninstall ← Uninstall self
  • download ← Download File
  • upload ← Upload File
  • enum-driver ← not used
  • enum-faf ← not used
  • enum-process ← Enumerate process
  • cmd-shell ← Command shell
  • exit-process ← Exit process
  • sleep ← Sleep malware
  • delete ← Delete File or Folder

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

  • http://{BLOCKED}her.no-ip.org:19002

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 12.946.07
FIRST VSAPI PATTERN DATE: 07 Dec 2016
VSAPI OPR PATTERN File: 12.947.00
VSAPI OPR PATTERN Date: 08 Dec 2016

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

Scan your computer with your Trend Micro product to delete files detected as VBS_SHELLEXE.AG. 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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