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RANSOM_CRYPWALL.YUYAHG

February 10, 2016
 Analysis by: Francis Xavier Antazo
 ALIASES:

Win32/Filecoder.CryptoWall.F (ESET); Trojan.Cryptodefense (Symantec); FileCryptor.GDP (AVG); Ransom.CryptoWall (Malwarebytes);

 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 itself after execution. It is capable of encrypting files in the affected system.

  TECHNICAL DETAILS

File Size:

27,136 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

07 Feb 2016

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:

  • %Desktop%\HELP_YOUR_FILES.TXT
  • %Desktop%\HELP_YOUR_FILES.HTML
  • %Desktop%\HELP_YOUR_FILES.PNG

(Note: %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.)

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

  • %Application Data%\{random characters}\{random characters}.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.)

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} = "%Application Data%\{random characters}\{random characters}.exe"

Other System Modifications

This Trojan modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SystemRestore
DisableSR = "1"

(Note: The default value data of the said registry entry is "0".)

Dropping Routine

This Trojan drops the following files:

  • HELP_YOUR_FILES.PNG - drops to all folders where files are encrypted
  • %User Startup%\HELP_YOUR_FILES.TXT
  • %User Startup%\HELP_YOUR_FILES.HTML
  • %User Startup%\HELP_YOUR_FILES.PNG

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Documents and Settings\{user}\Start Menu\Programs\Startup on Windows 2000 and XP, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup on Windows Vista, 7, and 8.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • {BLOCKED}l.kz/dHzBrf.php
  • {BLOCKED}ecor.com.br/2LfPSn.php
  • {BLOCKED}anfinance33.tk/OZWKU0.php
  • {BLOCKED}antonenko.tk/kYvR76.php
  • {BLOCKED}arier.in/CzYsIX.php
  • {BLOCKED}n-petrov.su/K_jLJD.php
  • {BLOCKED}ry.tk/Lm6gSf.php
  • {BLOCKED}de.it/QUW32z.php
  • {BLOCKED}on.tk/o28_a9.php
  • {BLOCKED}s-hub.in/PxyNoi.php
  • {BLOCKED}er.tk/R0iCvm.php
  • {BLOCKED}ouse.nl/ISj7Hc.php
  • {BLOCKED}mp.org/9Wdolt.php
  • {BLOCKED}cious.ie/UWxJIT.php
  • {BLOCKED}hirts.us/zVnMrG.php
  • {BLOCKED}avskaia.com/MmDZHb.php
  • {BLOCKED}avskaia.com/MmDZHb.php
  • {BLOCKED}puterservices.com.au/S1_rvm.php
  • {BLOCKED}ondmina.com.br/uweBiP.php
  • {BLOCKED}port.kiev.ua/z8X9T7.php
  • {BLOCKED}k.in/3QVrlo.php
  • {BLOCKED}nsetminimalis.tk/uG9evX.php
  • {BLOCKED}heels.com/HDen4L.php
  • {BLOCKED}che.com/ibXxOG.php
  • {BLOCKED}a.pl/RsCIjo.php
  • {BLOCKED}obraga.com.br/OnbrsQ.php
  • {BLOCKED}ct.pl/TBP8hn.php
  • {BLOCKED}ger.pl/qKdlCr.php
  • {BLOCKED}tyclassifieds.com/YubGna.php
  • {BLOCKED}yconsignment.com/5x1kZJ.php
  • {BLOCKED}hrentals.co.za/Sj4C0t.php
  • {BLOCKED}b.in.ua/tV6qyl.php
  • {BLOCKED}kmanagementsoftware0305.tk/v29Uyo.php
  • {BLOCKED}likesuka.com/YseuV3.php
  • {BLOCKED}n.com.ua/3VHGmB.php
  • {BLOCKED}ivoalluminio.it/OSPgcI.php
  • {BLOCKED}emenu.com/BLe5wG.php
  • {BLOCKED}ossa.com.br/M81UVu.php
  • {BLOCKED}ice.com.ua/_ALErU.php
  • {BLOCKED}r.remsop.com/awDmPT.php
  • {BLOCKED}polyglot.com/OvLNMq.php
  • {BLOCKED}rma.com/WMGtck.php
  • {BLOCKED}9.org/8UmXhY.php
  • {BLOCKED}diti.com.ua/d6yGOX.php
  • {BLOCKED}ssedbee.co.uk/CPsVa0.php
  • {BLOCKED}paz.co.za/drDLa4.php
  • {BLOCKED}uentoaqui.cl/qsJfPu.php

It renames encrypted files using the following names:

  • {random characters}.{random characters}

It deletes itself after execution.

It is capable of encrypting files in the affected system.

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

12.282.07

FIRST VSAPI PATTERN DATE:

19 Jan 2016

VSAPI OPR PATTERN File:

12.283.00

VSAPI OPR PATTERN Date:

20 Jan 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} = "%Application Data%\{random characters}\{random characters}.exe"

Step 5

Restore this modified 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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SystemRestore
    • From: DisableSR = "1"
      To: DisableSR = "0"

Step 6

Search and delete these files

[ 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.
  • HELP_YOUR_FILES.TXT
  • HELP_YOUR_FILES.PNG
  • HELP_YOUR_FILES.HTML

Step 7

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


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