Analysis by: Francis Xavier Antazo
ALIASES:

a variant of Win32/Filecoder.DMALocker.A (ESET); Trojan-Ransom.Win32.Blocker.iadc (Kaspersky); Trojan.Ransomcrypt.AA (Symantec); Ransom.DMALocker (Malwarebytes); FileCryptor.GAV (AVG);

 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: Dropped by other malware, Downloaded from the Internet

This latest ransomware variant is dubbed as DMA Locker. It encrypts files on fixed, removable and network drives.

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 is capable of encrypting files in the affected system.

  TECHNICAL DETAILS

File Size: 97,824 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 16 Jan 2016
Payload: Encrypts files, Terminates processes

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 copies of itself into the affected system and executes them:

  • {variable path 1}\ntserver.exe

It drops the following file(s)/component(s):

  • {variable path 1}\data_1.txt -> contains the date when ransomware was executed
  • {variable path 1}\decrypting.txt
  • {variable path 1}\start.txt
  • {variable path 1}\cryptinfo.txt -> ransom note

It drops the following copies of itself into the affected system:

  • {variable path 1}\fakturax.exe

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
cssys = "{variable path 1}\ntserver.exe"

Other System Modifications

This Trojan adds the following registry entries:

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
cryptedinfo = "{variable path 1}\cryptinfo.txt"

Process Termination

This Trojan terminates the following processes if found running in the affected system's memory:

  • rstrui.exe
  • ShadowExplorer.exe
  • sesvc.exe
  • cbengine.exe

Other Details

This Trojan is capable of encrypting files in the affected system.

NOTES:

It avoids the following file paths:

  • \Windows\
  • \WINDOWS\
  • \Program Files\
  • \Program Files (x86)\
  • Games
  • \Temp
  • \Sample Pictures
  • \Sample Music
  • \cache
  • \Cache

It avoids the following file extensions:

  • .exe
  • .msi
  • .dll
  • .pif
  • .scr
  • .sys
  • .msp
  • .com
  • .lnk
  • .hta
  • .cpl
  • .msc
{variable path 1} may have the following values:
  • C:\ProgramData
  • %All Users Profile%\Dokumenty
  • %All Users Profile%

Once the Trojan is executed, it displays the following window:

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 12.318.08
FIRST VSAPI PATTERN DATE: 05 Feb 2016
VSAPI OPR PATTERN File: 12.319.00
VSAPI OPR PATTERN Date: 06 Feb 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

Restart in Safe Mode

[ Learn More ]

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.
  • {variable path 1}\data_1.txt
  • {variable path 1}\decrypting.txt
  • {variable path 1}\start.txt
  • {variable path 1}\cryptinfo.txt

Step 5

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_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • cssys = "{variable path 1}\ntserver.exe"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • cryptedinfo = "{variable path 1}\cryptinfo.txt"

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as RANSOM_MADLOCKER.B. 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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