Analysis by: Michael Jay Villanueva

 ALIASES:

Ransom.Enigma (Malwarebytes); Trojan.Ransom.Enigma.2 (Arcabit)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

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

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 executes then deletes itself afterward.

It modifies the Internet Explorer Zone Settings.

It connects to certain websites to send and receive information.

  TECHNICAL DETAILS

File Size: 260,608 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 17 Oct 2016
Payload: Encrypts files, Connects to URLs/IPs

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 files:

  • %User Temp%\pbkey.pbkey -> public key
  • %User Temp%\prkey.prkey -> private key
  • %User Temp%\enigma_info.txt -> Ransom Note
  • %User Temp%\workstatistic.dat
  • %User Temp%\falcon9.falcon
  • %Desktop%\E_N_I_G_M_A.RSA -> key file
  • %User Temp%\E_N_I_G_M_A.RSA -> key file

(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.. %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.)

It drops and executes the following files:

  • %Desktop%\enigma_info.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.)

It executes then deletes itself afterward.

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
bfceedddae = "{Malware Path}\{Malware Filename}.exe"

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://{BLOCKED}.{BLOCKED}.201.113/get.php

It encrypts files with the following extensions:

  • .001
  • .002
  • .1cd
  • .7z
  • .bz
  • .bz2
  • .bza
  • .bzip
  • .bzip2
  • .cd
  • .cdr
  • .crt
  • .csr
  • .csv
  • .czip
  • .dat
  • .dbf
  • .dif
  • .doc
  • .docb
  • .docm
  • .docx
  • .dwg
  • .gz
  • .gz
  • .gz2
  • .gza
  • .gzi
  • .gzip
  • .hdoc
  • .hwp
  • .key
  • .kwm
  • .lzma
  • .max
  • .mdb
  • .mdb
  • .mml
  • .odg
  • .odp
  • .ods
  • .odt
  • .odt
  • .otg
  • .otp
  • .ots
  • .ott
  • .pdf
  • .pem
  • .pot
  • .potm
  • .potx
  • .ppam
  • .pps
  • .ppsm
  • .ppsx
  • .ppt
  • .ppt
  • .pptm
  • .pptx
  • .pptx
  • .rar
  • .rtf
  • .rtf
  • .slk
  • .sln
  • .sqlite
  • .sqx
  • .sqz
  • .srep
  • .stc
  • .std
  • .sti
  • .stw
  • .sxc
  • .sxi
  • .sxm
  • .sxw
  • .tar
  • .taz
  • .tbz
  • .tbz2
  • .tg
  • .tgz
  • .tlz
  • .tlzma
  • .tsk
  • .tx_
  • .txt
  • .txz
  • .tz
  • .uc2
  • .uot
  • .wks
  • .xlc
  • .xlm
  • .xls
  • .xlsb
  • .xlsm
  • .xlsx
  • .xlsx
  • .xlt
  • .xltm
  • .xltx
  • .xlw
  • .xz
  • .zi
  • .zip
  • .zip
  • .zipx
  • .zix

It renames encrypted files using the following names:

  • {Original Filename and Extension}.1txt
    • ie. Sample.txt.1txt

It does the following:

  • It deletes shadow copies by executing the following command:
    • vssadmin delete shadows /all /quiet

NOTES:

It drops the following ransom note:

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 12.842.03
FIRST VSAPI PATTERN DATE: 17 Oct 2016
VSAPI OPR PATTERN File: 12.843.00
VSAPI OPR PATTERN Date: 18 Oct 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

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
    • bfceedddae = "{Malware Path}\{Malware Filename}.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.
  • %User Temp%\pbkey.pbkey
  • %User Temp%\prkey.prkey
  • %User Temp%\enigma_info.txt
  • %User Temp%\workstatistic.dat
  • %User Temp%\falcon9.falcon
  • %User Temp%\E_N_I_G_M_A.RSA
  • %Desktop%\E_N_I_G_M_A.RSA
  • %Desktop%\enigma_info.txt

Step 6

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

Step 7

Reset Internet security settings

[ Learn More ]


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