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RANSOM_LOCKY

July 06, 2016
 ALIASES:

Ransom:Win32/Locky!rfn (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

Infection Channel:

Downloaded from the Internet


This ransomware arrives via spam with macro-embedded .DOC attachment, similar to the arrival of DRIDEX malware.

It renames encrypted files to the format {unique ID per victim}{identifier}.locky.

This Trojan may be unknowingly downloaded by a user while visiting malicious websites.

It modifies the Internet Explorer Zone Settings.

It connects to certain websites to send and receive information.

  TECHNICAL DETAILS

File Size:

165,888 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

24 Feb 2016

Payload:

Drops files, Encrypts files

Arrival Details

This Trojan may be unknowingly downloaded by a user while visiting malicious websites.

Installation

This Trojan drops the following copies of itself into the affected system and executes them:

  • %User Temp%\svchost.exe - This is deleted after encryption of files

(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.)

It drops the following component file(s):

  • %Desktop%\_Locky_recover_instructions.txt - ransom note
  • %Desktop%\_Locky_recover_instructions.bmp - image used as wallpaper
  • {Folders containing encrypted files}\_Locky_recover_instructions.txt - ransom note

(Note: %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.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Locky = "%User Temp%\svchost.exe"

(Note: This registry entry is deleted after encryption of all files)

Other System Modifications

This Trojan modifies the following file(s):

  • It renames the encrypted files to {unique ID per victim}{identifier}.locky

It adds the following registry keys:

HKEY_CURRENT_USER\Software\Locky

It adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\Locky
id = "{unique ID per victim}"

HKEY_CURRENT_USER\Software\Locky
pubkey = "{publick key}"

HKEY_CURRENT_USER\Software\Locky
paytext = "{ransom note}"

HKEY_CURRENT_USER\Software\Locky
completed = "1"

Web Browser Home Page and Search Page Modification

This Trojan modifies the Internet Explorer Zone Settings.

Other Details

This Trojan connects to the following website to send and receive information:

  • http://{URL list depending on variant}/main.php

It encrypts files with the following extensions:

  • .ARC
  • .CSV
  • .DOC
  • .DOT
  • .MYD
  • .MYI
  • .NEF
  • .PAQ
  • .PPT
  • .RTF
  • .SQLITE3
  • .SQLITEDB
  • .XLS
  • .aes
  • .asc
  • .asf
  • .asm
  • .asp
  • .avi
  • .bak
  • .bat
  • .bmp
  • .brd
  • .bz2
  • .cgm
  • .class
  • .cmd
  • .cpp
  • .crt
  • .csr
  • .dbf
  • .dch
  • .dif
  • .dip
  • .djv
  • .djvu
  • .docb
  • .docm
  • .docx
  • .dotm
  • .dotx
  • .fla
  • .flv
  • .frm
  • .gif
  • .gpg
  • .hwp
  • .ibd
  • .jar
  • .java
  • .jpeg
  • .jpg
  • .key
  • .lay
  • .lay6
  • .ldf
  • .max
  • .mdb
  • .mdf
  • .mid
  • .mkv
  • .mml
  • .mov
  • .mpeg
  • .mpg
  • .ms11
  • .odb
  • .odg
  • .odp
  • .ods
  • .odt
  • .otg
  • .otp
  • .ots
  • .ott
  • .pas
  • .pdf
  • .pem
  • .php
  • .png
  • .pot
  • .potm
  • .potx
  • .ppam
  • .pps
  • .ppsm
  • .ppsx
  • .pptm
  • .pptx
  • .psd
  • .qcow2
  • .rar
  • .raw
  • .sch
  • .sldm
  • .sldx
  • .slk
  • .sql
  • .stc
  • .std
  • .sti
  • .stw
  • .svg
  • .swf
  • .sxc
  • .sxd
  • .sxi
  • .sxm
  • .sxw
  • .tar
  • .tbk
  • .tgz
  • .tif
  • .tiff
  • .txt
  • .uop
  • .uot
  • .vbs
  • .vdi
  • .vmdk
  • .vmx
  • .vob
  • .wav
  • .wks
  • .wma
  • .wmv
  • .xlc
  • .xlm
  • .xlsb
  • .xlsm
  • .xlsx
  • .xlt
  • .xltm
  • .xltx
  • .xlw
  • .xml
  • .zip
  • wallet.dat

It does the following:

  • It prevents to encrypt files containing any of the strings in its full pathname:
    • AppData
    • Application Data
    • Program Files
    • temp
    • $Recycle.Bin
    • System Volume Information
    • Boot
    • Windows
    • winnt
    • thumbs.db
  • After encryption of files, it uninstalls itself by deleting its autorun registry and its copy.
  • It executes the following command to delete shadow copies:

    vssadmin.exe Delete Shadows /All /Quiet

NOTES:

This malware sets the system's desktop wallpaper to the following image:

It opens the dropped _Locky_recover_instructions.txt, which contains the ransom note:

  SOLUTION

Minimum Scan Engine:

9.800

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
    • Locky = "%User Temp%\svchost.exe"
  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • Wallpaper = "%Desktop%\_Locky_recover_instructions.bmp"

Step 5

Delete this registry key

[ 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
    • Locky

Step 6

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.
  • %Desktop%\_Locky_recover_instructions.txt
  • %Desktop%\_Locky_recover_instructions.bmp
  • {Folders containing encrypted files}\_Locky_recover_instructions.txt

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as RANSOM_LOCKY. 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 8

Restore encrypted files from backup.

Step 9

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