RANSOM_CERBER.VSAFS

 Analysis by: Warren Adam Sto. Tomas

 ALIASES:

Trojan-Ransom.Win32.Zerber.bwfc(Kaspersky); Trojan:Win32/Dynamer!ac(Microsoft)

 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

File Size:

245,505 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

13 Feb 2017

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:

  • %User Temp%\tmp{random characters}.bmp - Background Image
  • {folders containing encrypted files}\_HELP_HELP_HELP_{random characters}_.hta - Ransome Instructions
  • {folders containing encrypted files}\_HELP_HELP_HELP_{random characters}_.png - Ransom Note
  • %Desktop%\_HELP_HELP_HELP_{random characters}_.hta
  • %Desktop%\_HELP_HELP_HELP_{random characters}_.png
  • {malware path}\_HELP_HELP_HELP_{random characters}_.hta
  • {malware path}\_HELP_HELP_HELP_{random characters}_.png
  • %User Temp%\{8 random characters}\{4 random characters}.tmp
  • %User Temp%\{8 random characters}\{4 random characters}.tmp

(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.. %Desktop% is the desktop folder, where it usually is C:\Documents and Settings\{user name}\Desktop in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\Desktop in 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.)

It creates the following folders:

  • %User Temp%\{8 random characters}

(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{random characters}.bmp

(Note: The default value data of the said registry entry is {User defined}.)

Other Details

This Trojan renames encrypted files using the following names:

  • {10 random characters}.{4 random characters}

It does the following:

  • It speaks the following text using text-to-speech application:
    • "Attention! Attention! Attention! Your documents, photos, databases and other important files have been encrypted!"

It deletes the initially executed copy of itself

It is capable of encrypting files in the affected system.

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

13.218.06

FIRST VSAPI PATTERN DATE:

13 Feb 2017

VSAPI OPR PATTERN File:

13.219.00

VSAPI OPR PATTERN Date:

14 Feb 2017

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

Search and delete these folders

[ 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%\{8 random characters}

Step 4

Search and delete this file

[ 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%\tmp{random characters}.bmp - Background Image
  • {folders containing encrypted files}\_HELP_HELP_HELP_{random characters}_.hta
  • {folders containing encrypted files}\_HELP_HELP_HELP_{random characters}_.png
  • %Desktop%\_HELP_HELP_HELP_{random characters}_.hta
  • %Desktop%\_HELP_HELP_HELP_{random characters}_.png
  • {malware path}\_HELP_HELP_HELP_{random characters}_.hta
  • {malware path}\_HELP_HELP_HELP_{random characters}_.png

Step 5

Reset your Desktop properties

[ Learn More ]

Step 6

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

Step 7

Restore encrypted files from backup.


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