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RANSOM_CRYPTESLA.CBQ163M

April 06, 2016
 Analysis by: Jeanne Jocson
 ALIASES:

Ransom:Win32/Tescrypt!rfn(Microsoft), Win32/Filecoder.TeslaCrypt.K(ESET), Trojan.Cryptolocker.N(Norton)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

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 the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

368,640 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

22 Mar 2016

Payload:

Connects to URLs/IPs, 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 the following copies of itself into the affected system and executes them:

  • %My Documents%\{random filename}.exe

    (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.)

It drops the following files:

  • Ransom notes:
    • {folders containing encrypted files}\+REcovER+{random 5 characters}.txt
    • {folders containing encrypted files}\+REcovER+{random 5 characters}.png
    • {folders containing encrypted files}\+REcovER+{random 5 characters}.html
    • %Desktop%\+REcovER+{random 5 characters}.txt
    • %Desktop%\+REcovER+{random 5 characters}.png
    • %Desktop%\+REcovER+{random 5 characters}.html
    • %My Documents%\+REcovER+{random 5 characters}.txt
    • %My Documents%\+REcovER+{random 5 characters}.png
    • %My Documents%\+REcovER+{random 5 characters}.html
  • %My Documents%\+recover+file.txt

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 %My Documents%\{random filename}.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\trueimg

HKEY_CURRENT_USER\Software\{ID}

HKEY_USERS\.DEFAULT\Software\
trueimg

It adds the following registry entries as part of its installation routine:

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

To enable Windows to share network connections

HKEY_CURRENT_USER\Software\trueimg
ID = "{ID}"

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

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}s.org/phsys.php
  • http://{BLOCKED}bow.com/phsys.php
  • http://{BLOCKED}entrausaha.com/phsys.php
  • http://{BLOCKED}legue.com/phsys.php
  • http://classemgmt.{BLOCKED}da.com/phsys.php

It does the following:

  • It encrypts files in all fixed, removable, and network drives and shares.
  • It does not append an extension to the encrypted files.
  • It deletes shadow copies

It deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

12.418.08

FIRST VSAPI PATTERN DATE:

22 Mar 2016

VSAPI OPR PATTERN File:

12.419.00

VSAPI OPR PATTERN Date:

23 Mar 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

Scan your computer with your Trend Micro product and note files detected as RANSOM_CRYPTESLA.CBQ163M

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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

    • Step 6

    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
      • trueimg
    • In HKEY_CURRENT_USER\Software
      • {ID}

    Step 7

    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.
    • %My Documents%\+recover+file.txt
    • +REcovER+{random 5 characters}.txt
    • +REcovER+{random 5 characters}.png
    • +REcovER+{random 5 characters}.html

    Step 8

    Restart in normal mode and scan your computer with your Trend Micro product for files detected as RANSOM_CRYPTESLA.CBQ163M. 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 9

    Restore encrypted files from backup.


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