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RANSOM_CERBER.AUSIZ

September 26, 2017
 Analysis by: Jeanne Jocson
 ALIASES:

Trojan-Ransom.Win32.Zerber.ahgy (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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.

It deletes the initially executed copy of itself. It is capable of encrypting files in the affected system.

  TECHNICAL DETAILS

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 the following files:

  • {folders containing encrypted files}\README.hta - Ransom Note
  • %User Temp%\{tmp filename}.bmp - background image

(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.)

Other System Modifications

This Trojan changes the desktop wallpaper by modifying the following registry entries:

HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = %User Temp%\{tmp filename}.bmp

Other Details

This Trojan renames encrypted files using the following names:

  • {10 Random Characters}.{4 Random Characters}

It does the following:

  • It deletes all shadow copies by executing the following command:
    • WMIC.exe shadowcopy delete

It deletes the initially executed copy of itself

It is capable of encrypting files in the affected system.

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

12.928.05

FIRST VSAPI PATTERN DATE:

23 Nov 2016

VSAPI OPR PATTERN File:

12.929.00

VSAPI OPR PATTERN Date:

24 Nov 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

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

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\Control Panel\Desktop
    • Wallpaper = %User Temp%\tmp8D.bmp

Step 4

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.  
  • {folders containing encrypted files}\README.hta
  • %User Temp%\{tmp filename}.bmp

Step 5

Reset your Desktop properties

[ Learn More ]

Step 6

Restore encrypted files from backup.

Step 7

Scan your computer with your Trend Micro product to delete files detected as RANSOM_CERBER.AUSIZ. 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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