Analysis by: Patrick Angelo Roderno
ALIASES:

Trojan-Ransom.Win32.Matrix.in (KASPERSKY); Ransom.CryptXXX (NORTON); Ransom:Win32/Delcryset.A (MICROSOFT)

 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: Dropped by other malware, Downloaded from the Internet

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.

  TECHNICAL DETAILS

File Size: 910,848 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 11 Sep 2017
Payload: Drops files, Displays graphics/image, Encrypts files

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 mutexes to ensure that only one of its copies runs at any one time:

  • OurMainMutex007

File Infection

This Ransomware searches for target files in the following drives:

  • Z:\
  • Y:\
  • X:\
  • W:\
  • V:\
  • U:\
  • T:\
  • S:\
  • R:\
  • Q:\
  • P:\
  • O:\
  • N:\
  • M:\
  • L:\
  • K:\
  • J:\
  • I:\
  • H:\
  • G:\
  • F:\
  • E:\
  • D:\
  • C:\

Dropping Routine

This Ransomware drops the following files:

  • flist.lst -> list of files to be encrypted
  • {Personal ID}.pkey -> personal ID generated by the ransomware
  • {Personal ID}.skey -> personal ID generated by the ransomware
  • errlog.txt -> error logs of the ransomware

Other Details

This Ransomware does the following:

  • Grants access rights of files to the current user
  • Clears the read-only, archive, and hidden attribute assigned to files
  • Prioritizes the encryption of files with the following extensions:
    • .1cd
    • .dt
    • .dbf
    • .dbx
    • .mdb
    • .mdf
    • .sdf
    • .accdb
    • .zip
    • .rar
    • .7z
    • .xlsx
    • .xls
    • .docx
    • .doc
    • .rtf
    • .ods
    • .odt
    • .pdf
    • .jpg
    • .jpeg
    • .txt

Ransomware Routine

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

  • .locked_file
  • .lst
  • .pkey
  • .skey
  • .lnk
  • .exe
  • .tmp
  • .ico
  • .000
  • .sys
  • .dat
  • .inf
  • .dll
  • .dat
  • .reg
  • .drv
  • .dev
  • .pif
  • .mbr
  • .ini
  • .xml
  • .list
  • .ttf
  • .log
  • .ja
  • .bat
  • .cmd
  • .vbs
  • .js
  • .cfg
  • .download
  • .nfo
  • .msi
  • .chk
  • .dmp
  • .mui
  • .dun
  • .isp
  • .isw
  • .cab
  • .efi
  • .hlp
  • .msu
  • .hlp
  • .bin
  • .lng
  • .torrent_info
  • .torrent
  • .htm
  • .html
  • .chm
  • .lang
  • .style
  • .gif
  • .java
  • .cur
  • .ani

It avoids encrypting files with the following strings in their file path:

  • \WINDOWS
  • \PROGRAM FILES
  • \GAMES
  • \APPDATA
  • \APPLICATION DATA
  • \PROGRAMDATA
  • \LOCAL SETTINGS
  • \TEMP
  • \TMP
  • \BOOT
  • \MSOCACHE
  • \DEFAULT USER
  • \SAMPLE
  • \EXAMPLE
  • \I386
  • \TEMPORARY
  • \TOR BROWSER
  • \BROWSER
  • BROWSER\

It renames encrypted files using the following names:

  • {Random Characters}.[{BLOCKED}eassistant2@{BLOCKED}a.com].locked_file -> random characters generated by the ransomware

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

  • !HOW_TO_UNLOCK_FILES!.html

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 13.654.08
FIRST VSAPI PATTERN DATE: 11 Sep 2017
VSAPI OPR PATTERN File: 13.655.00
VSAPI OPR PATTERN Date: 12 Sep 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

Identify and terminate files detected as RANSOM_LOCKED.A

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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.
  • flist.lst
  • {Personal ID}.pkey
  • {Personal ID}.skey
  • errlogs.txt
  • !HOW_TO_UNLOCK_FILES!.html

Step 5

Scan your computer with your Trend Micro product to delete files detected as RANSOM_LOCKED.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 6

Restore encrypted files from backup.


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