RANSOM_CRYPTESLA.SMK4

April 07, 2017
 Analysis by: Pearl Charlaine Espejo
 ALIASES:

Ransom:Win32/Tescrypt.A (Microsoft); TR/AD.TeslaCrypt.Y.392 (Avira); Trojan/Win32.Teslacrypt.R176153 (AhnLab-V3)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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 the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

480,256 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

04 Apr 2017

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:

  • %Windows%\{random filename}.exe (with Administrator Privileges)
  • %My Documents%\{random filename}.exe (with non-Administrator Privileges)

    (Note: %My Documents% is usually C:\Documents and Settings\{user name}\My Documents on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\Documents on Windows Vista and 7.)

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

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
{random characters} = "%System%\CMD.EXE /C START %Windows%\{random filename}.exe" (with Administrator Privileges)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random characters} = "%System%\CMD.EXE /C START %My Documents%\{random filename}.exe" (with non-Administrator Privileges)

Other System Modifications

This Trojan modifies the following file(s):

  • It encrypts files in all fixed, removable, and network drives and shares.
  • It adds the extension .mp3 to the encrypted files

It adds the following registry keys:

HKEY_CURRENT_USER\Software\zzzsys

HKEY_CURRENT_USER\Software\{ID}

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
EnableLinkedConnections = "1"

HKEY_CURRENT_USER\Software\zzzsys
ID = "{random values}"

HKEY_CURRENT_USER\Software\{ID}
data = "{random values}"

Dropping Routine

This Trojan drops the following files:

  • %User Profile%\My Documents\recover_file_{random}.txt
  • %Desktop%\_ReCoVeRy_.TXT
  • %Desktop%\_ReCoVeRy_.HTM
  • %Desktop%\_ReCoVeRy_.png
  • {folders containing encrypted files}\_ReCoVeRy_+{random}.png
  • {folders containing encrypted files}\_ReCoVeRy_+{random}.txt
  • {folders containing encrypted files}\_ReCoVeRy_+{random}.html

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %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.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}edicalcentre.com/wp-content/uploads/wstr.php
  • http://{BLOCKED}ur.info/users/28c4fe1/wstr.php
  • http://{BLOCKED}stitut.org/wp-content/themes/bstr.php
  • http://{BLOCKED}lizedaccess.co.uk/wp-content/uploads/2015/09/wstr.php
  • http://www.{BLOCKED}aticauno.net/gamma/tmp/bstr.php

It deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

12.450.06

FIRST VSAPI PATTERN DATE:

06 Apr 2016

VSAPI OPR PATTERN File:

12.451.00

VSAPI OPR PATTERN Date:

07 Apr 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
    • {random characters} = "%System%\CMD.EXE /C START %My Documents%\{random filename}.exe" (with non-Administrator Privileges)
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {random characters} = "%System%\CMD.EXE /C START %Windows%\{random filename}.exe" (with Administrator Privileges)
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system
    • EnableLinkedConnections = "1"

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
    • zzzsys
  • In HKEY_CURRENT_USER\Software
    • {ID}

Step 6

Search and delete these components

[ Learn More ]
There may be some components 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.
  • _ReCoVeRy_+{random}.png
  • _ReCoVeRy_+{random}.txt
  • _ReCoVeRy_+{random}.html
  • %Desktop%\_ReCoVeRy_.png
  • %Desktop%\_ReCoVeRy_.HTM
  • %Desktop%\_ReCoVeRy_.TXT
  • %User Profile%\My Documents\recover_file_{random}.txt

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as RANSOM_CRYPTESLA.SMK4. 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.


Did this description help? Tell us how we did.