Analysis by: Julie Anne Cabuhat
ALIASES:

BAT/LockFiles.C!tr (Fortinet), Ransom:Win32/Blobash.A (Microsoft)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

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

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 is capable of encrypting files in the affected system.

  TECHNICAL DETAILS

File Size: 92,160 bytes
File Type: EXE
File Compression: UPX
Memory Resident: No
Initial Samples Received Date: 10 Nov 2016
Payload: Encrypts files

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 and executes the following files:

  • %User Temp%\{random characters}.tmp\Cod3r_ZH.bat - deletes itself after execution

(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.)

Dropping Routine

This Trojan drops the following files:

  • {malware path}\{4 random characters}\info.txt - contains text in messagebox
  • {malware path}\{4 random characters}\CH.txt
  • {malware path}\LOCK.rar - contains encrypted files

Other Details

This Trojan does the following:

  • It uses WinRAR.exe to encrypt the files using the following command:
    • "%Program Files%\WinRAR\Rar.exe" a -r -y -ri15 -df -m0 -inul -p"{password}" "LOCK.rar"
  • The parameters meaning the following:
    • a - add files to archive
    • r - recurse subdirectories
    • y - assume Yes on all queries
    • df - delete files after archiving
    • m0 - set compression level to 0
    • inul - Disable all messages
    • p- set password

(Note: %Program Files% is the Program Files folder, where it usually is C:\Program Files on all Windows operating system versions; C:\Program Files (x86) for 32-bit applications running on Windows 64-bit operating systems.)

It is capable of encrypting files in the affected system.

NOTES:

Based on the analysis of codes, it has other capabilities than was not exhibited due to the batch file deleting itself.

It uses "118095" as the password. The ransomware displays the following ransomnote:

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 12.890.08
FIRST VSAPI PATTERN DATE: 10 Nov 2016
VSAPI OPR PATTERN File: 12.891.00
VSAPI OPR PATTERN Date: 11 Nov 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

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.  
  • %User Temp%\{4 random characters}.tmp\Cod3r_ZH.bat
  • {malware path}\{4 random characters}\info.txt
  • {malware path}\{4 random characters}\CH.txt

Step 4

Scan your computer with your Trend Micro product to delete files detected as RANSOM_RARLOCK.F116KA. 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 5

Restore encrypted files from backup.


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