Analysis by: Ryan Gardo
ALIASES:

W97M/Generic(AVG); MW97:Downloader-AI [Trj](Avast); W97M.Downloader(Symantec)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Via email

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

  TECHNICAL DETAILS

File Size: 72,704 bytes
File Type: DOC
Memory Resident: No
Initial Samples Received Date: 19 Feb 2015
Payload: Connects to URLs/IPs, Downloads files

Arrival Details

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

NOTES:

Once the malicous document is opened, the macro which contains the malware code executes and drops the following files:

  • For Windows XP and below:
    • %Temp%\3gysajdg.tmp
    • %Temp%\adobeacd-update.bat
    • %Temp%\adobeacd-updatexp.vbs
  • For Windows Vista and above:
    • %User Temp%\adobeacd-update.vbs
    • %User Temp%\adobeacd-update.bat
    • %User Temp%\adobeacd-update.ps1

The file adobeacd-updatexp.vbs and adobeacd-update.ps1 accesses the following links to download files:

  • http://{BLOCKED}c.su/5051050.png - Windows XP and below
  • http://{BLOCKED}c.su/5106349.png - Windows Vista and above
  • http://{BLOCKED}.{BLOCKED}.131.49/upd2/install.exe

The malware saves the file using the following file name:

  • %Temp%\444.exe - Windows XP and below
  • %User Temp%\444.exe - Windows Vista and above
  • %User Temp%\444.png - Windows Vista and above

On Windows XP and below, the file adobeacd-update.bat executes adobeacd-updatexp.vbs and the downloaded file %Temp\444.exe%. It also deletes itself after execution.

On Windows Vista and above, the file adobeacd-update.bat executes adobeacd-update.vbs which in turn executes adobeacd-update.ps1. The file adobeacd-update.ps1 ensures that the downloaded file is executed and deletes all dropped files after execution.

As of this writing, the URL http://{BLOCKED}.{BLOCKED}.131.49/upd2/install.exe is inaccessible.

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.490.02
FIRST VSAPI PATTERN DATE: 20 Feb 2015
VSAPI OPR PATTERN File: 11.491.00
VSAPI OPR PATTERN Date: 21 Feb 2015

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

Search and delete these components

[ Learn More ]
There may be some components 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.
  • %Temp%\444.exe (For OS Version XP and below)
  • %Temp%\3gysajdg.tmp (For OS Version XP and below)
  • %Temp%\adobeacd-update.bat (For OS Version XP and below)
  • %Temp%\adobeacd-updatexp.vbs (For OS Version XP and below)
  • %User Temp%\444.exe (For OS Version Vista and above)
  • %User Temp%\adobeacd-update.vbs (For OS Version Vista and above)
  • %Temp%\adobeacd-update.bat (For OS Version Vista and above)
  • %Temp%\adobeacd-update.ps1 (For OS Version Vista and above)

Step 3

Scan your computer with your Trend Micro product to delete files detected as W2KM_BARTALEX.N. 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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