RANSOM_TROLDESH.THEBAAH

May 28, 2018
 Analysis by: Maureen Reyes
 ALIASES:

Ransom:Win32/Troldesh.A (Microsoft), HEUR:Trojan.Win32.Generic (Kaspersky), Win32/Filecoder.ED (ESET-NOD32)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

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 drops files as ransom note.

  TECHNICAL DETAILS

File Size:

962,048 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

21 May 2018

Payload:

Drops files, Deletes files

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:

  • %Temp%\6893A5D897\unverified-microdesc-consensus.tmp
  • %Temp%\6893A5D897\cached-certs.tmp
  • %Temp%\6893A5D897\cached-microdesc-consensus.tmp
  • %Temp%\6893A5D897\cached-microdesc.new
  • %Temp%\6893A5D897\lock
  • %Temp%\6893A5D897\state.tmp

(Note: %Temp% is the Windows temporary folder, where it usually is C:\Windows\Temp on all Windows operating system versions.)

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

  • %System Root%\Users\All Users\Windows\csrss.exe
  • %Program Data%\Windows\csrss.exe

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.)

It creates the following folders:

  • %System Root%\Users\All Users\Windows
  • %Program Data%\Windows
  • %Temp%\6893A5D897

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %Temp% is the Windows temporary folder, where it usually is C:\Windows\Temp on all Windows operating system versions.)

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
Client Server Runtime Subsystem = "%Program Data%\Windows\csrss.exe"

Other System Modifications

This Ransomware deletes the following files:

  • %Temp%\6893A5D897\unverified-microdesc-consensus.tmp

(Note: %Temp% is the Windows temporary folder, where it usually is C:\Windows\Temp on all Windows operating system versions.)

It adds the following registry entries:

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
xVersion = 4.0.0.1

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
xmail = 1

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
xmode = 0

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
xpk = {Random Alphanumeric}

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
xstate = 4

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
xcnt = 0

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
shst = 3

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
sh1 = {Random Alphanumeric}

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
sh2 = {Random Alphanumeric}

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
shsnt = 1

HKEY_LOCAL_MACHINE\Software\System32\
Configuration
xi = {Random Alphanumeric}

Ransomware Routine

This Ransomware appends the following extension to the file name of the encrypted files:

  • .crypted000007

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

  • {Fixed and Removable Drive Letter}:\README{1-10}.txt

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.264.03

FIRST VSAPI PATTERN DATE:

02 Mar 2018

VSAPI OPR PATTERN File:

14.265.00

VSAPI OPR PATTERN Date:

03 Mar 2018

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
    • Client Server Runtime Subsystem = "%Program Data%\Windows\csrss.exe"
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • xi = "{Random Alphanumeric}
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • xVersion value = "4.0.0.1"
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • xmail = "1"
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • xmode = "0"
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • xpk = "{Random Alphanumeric"
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • xstate = "4"
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • xcnt = "0"
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • shst = "3"
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • sh1 = "{Random Alphanumeric"}
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • sh2 = "{Random Alphanumeric"}
  • In HKEY_LOCAL_MACHINE\Software\System32\Configuration
    • shsnt = "1"

Step 5

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %System Root%\Users\All Users\Windows
  • %Program Data%\Windows
  • %Temp%\6893A5D897

Step 6

Scan your computer with your Trend Micro product to delete files detected as RANSOM_TROLDESH.THEBAAH. 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 the following Trend Micro Support pages for more information:

Step 7

Restore encrypted files from backup.


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