RANSOM_ISHTAR.A

 Analysis by: Homer Pacag

 ALIASES:

W32/Autoit.BR!tr (Fortinet); a variant of Win32/Filecoder.Ishtar.A (ESET-NOD32);

 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:

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 deletes itself after execution.

  TECHNICAL DETAILS

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

04 Nov 2016

Payload:

Encrypts files, Displays message/message boxes

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 copies of itself into the affected system and executes them:

  • %Application Data%\wintrish.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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 files:

  • {Malware Path}\{Malware Name}.docx
  • Application Data\ISHTAR.DATA
  • Application Data\README-ISHTAR.txt - ransom note
  • {Drive Letter}:\ISHTAR.DATA
  • {Drive Letter}:\README-ISHTAR.txt - ransom note

Autostart Technique

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

HKCU\Software\Microsoft\
Windows\CurrentVersion\Run
null = %Application Data%\wintrish.exe

Other System Modifications

This Trojan modifies the following file(s):

  • It encrypts files and renames into "ISHTAR-"{Original Filename}

It adds the following registry entries:

HKCU\Software\Ishtr 1.0
Start = Success

Other Details

This Trojan deletes itself after execution.

NOTES:

This ransomware locks the computer screen as shown below:

It displays the following ransom note:

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

12.878.08

FIRST VSAPI PATTERN DATE:

05 Nov 2016

VSAPI OPR PATTERN File:

12.879.00

VSAPI OPR PATTERN Date:

05 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

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
    • null = %Application Data%\wintrish.exe
  • In HKEY_CURRENT_USER\Software\Ishtr 1.0
    • Start = Success

Step 5

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.
  • %Application Data%\wintrish.exe
  • \{Malware Path}\{Malware Name}.docx
  • Application Data\ISHTAR.DATA
  • Application Data\README-ISHTAR.txt
  • {Drive Letter}:\ISHTAR.DATA
  • {Drive Letter}:\README-ISHTAR.txt

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as RANSOM_ISHTAR.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 this Knowledge Base page for more information.

Step 7

Restore encrypted files from backup.


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