Ransom.Win32.XCRY.THOAAHAI

March 07, 2019
 Analysis by: Jay Garcia
 ALIASES:

Win32:Trojan-gen (Avast); Trojan-Ransom.Win32.Encoder.bgq (Kaspersky)

 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 deletes itself after execution.

It encrypts files with specific file extensions. It drops files as ransom note.

  TECHNICAL DETAILS

File Size:

446,018 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

11 Jan 2019

Payload:

Deletes self after execution

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 drops the following files:

  • %Application Data%\encryption_key
  • %Application Data%\lock_file

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, and 8.)

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

  • %Application Data%\{random string}.exe

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, and 8.)

It adds the following processes:

  • ping {BLOCKED}.{BLOCKED}.2.1 -n 1 -w 5000

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random string} = %Application Data%\{random string}.exe

Other Details

This Ransomware deletes itself after execution.

Ransomware Routine

This Ransomware encrypts files with the following extensions:

  • .7z
  • .accdb
  • .arw
  • .bat
  • .bay
  • .c
  • .cdr
  • .cpp
  • .cr2
  • .crw
  • .cs
  • .cs
  • .css
  • .csv
  • .db
  • .dcr
  • .dng
  • .doc
  • .docx
  • .dpr
  • .dpr
  • .dump
  • .dwg
  • .dxf
  • .erf
  • .h
  • .h
  • .hpp
  • .html
  • .j
  • .jav
  • .java
  • .jpeg
  • .jpg
  • .js
  • .json
  • .jsp
  • .kdc
  • .lua
  • .lua
  • .m
  • .M
  • .mef
  • .mm
  • .mrw
  • .nef
  • .nrw
  • .orf
  • .pas
  • .pas
  • .pass
  • .pdf
  • .pef
  • .php
  • .php4
  • .php5
  • .pl
  • .pm
  • .png
  • .pod
  • .ppt
  • .pptx
  • .psd
  • .ptx
  • .py
  • .r3d
  • .raf
  • .rar
  • .raw
  • .rb
  • .rtf
  • .rw2
  • .rwl
  • .sql
  • .sr2
  • .srf
  • .srw
  • .svg
  • .t
  • .tar
  • .tar.gz
  • .tcl
  • .tiff
  • .txt
  • .vb
  • .vhd
  • .vhdx
  • .vmd
  • .vmdk
  • .wallet
  • .xls
  • .xlsx
  • .xml
  • .zip

It avoids encrypting files found in the following folders:

  • %Program Files%
  • %Windows%

(Note: %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000, Server 2003, and XP (32-bit), Vista (32-bit), 7 (32-bit), and 8 (32-bit), or C:\Program Files (x86) in Windows XP (64-bit), Vista (64-bit), 7 (64-bit), and 8 (64-bit).. %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

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

  • .xcry7684

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

  • HOW_TO_DECRYPT_FILES.html

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.759.00

FIRST VSAPI PATTERN DATE:

18 Jan 2019

VSAPI OPR PATTERN File:

14.760.00

VSAPI OPR PATTERN Date:

19 Jan 2019

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

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\Software\Microsoft\Windows\CurrentVersion\Run
    • {random string} = %Application Data%\{random string}.exe

Step 5

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.
  • %Application Data%\encryption_key
  • %Application Data%\lock_file
  • %Application Data%\{random string}.exe
  • {Encrypted Directory}\HOW_TO_DECRYPT_FILES.html

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.Win32.XCRY.THOAAHAI. 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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