Analysis by: Jemimah Mae Molina
ALIASES:

Ransom:Win32/PureLocker!MSR (MICROSOFT); TR/PureLocker.B (ANTIVIR)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

This Ransomware 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 files as ransom note. It avoids encrypting files with the following file extensions.

  TECHNICAL DETAILS

File Size: 86,528 bytes
File Type: DLL
Memory Resident: No
Initial Samples Received Date: 13 Nov 2019
Payload: Displays graphics/image

Arrival Details

This Ransomware 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 Ransomware adds the following processes:

  • wmic shadowstorage SET MaxSpace=337000000 → resizes the maximum amount of storage space that can be used for shadow copy storage

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • Global\{random characters}

Dropping Routine

This Ransomware drops the following files:

  • {Malware Path}\dbg.txt → contains list of files it was unable to encrypt

Ransomware Routine

This Ransomware avoids encrypting files with the following strings in their file name:

  • bootmgr
  • bootsect.bak
  • dbg.txt
  • iconcache.db
  • ntldr
  • ntuser.dat
  • thumbs.db
  • your_files.txt

It avoids encrypting files found in the following folders:

  • $Recycle.Bin
  • Boot
  • Google
  • Microsoft
  • Mozilla
  • MSOCache
  • Packages
  • Python27
  • Recycler
  • System Volume Information
  • Thunderbird

It appends the following extension to the file name of the encrypted files:

  • .CR1

It drops the following file(s) as ransom note:

  • {Encrypted Directory}\YOUR_FILES.txt

It avoids encrypting files with the following file extensions:

  • .qm
  • .dll
  • .exe
  • .ini
  • .sys
  • .lib
  • .msg
  • .ocx
  • .log
  • .url
  • .lnk
  • .cmd
  • .bat
  • .etl
  • .ico
  • .cpl
  • .wpl
  • .com
  • .inf
  • .msi
  • .mui
  • .hxw
  • .hxh
  • .oca
  • .dmp
  • .tmp
  • .chm
  • .hlp
  • .cr1
  • .readme
  • .manifest
  • .search-ms
  • .appref-ms
  • .library-ms
  • .searchconnector-ms
  • .old

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 15.492.04
FIRST VSAPI PATTERN DATE: 13 Nov 2019
VSAPI OPR PATTERN File: 15.493.00
VSAPI OPR PATTERN Date: 14 Nov 2019

Step 1

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 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 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.  
  • {Malware Path}\dbg.txt
  • {Encrypted Directory}\YOUR_FILES.txt

Step 4

Scan your computer with your Trend Micro product to delete files detected as Ransom.Win32.PURELOCKER.A. 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 the following Trend Micro Support pages for more information:

Step 5

Restore encrypted files from backup.


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