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TROJ_CRYPWALL.YK

August 07, 2015
 ALIASES:

Trojan horse FileCryptor.CLQ (AVG)

 PLATFORM:

Windows

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

  • 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.

  TECHNICAL DETAILS

File Size:

242,180 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

09 Jul 2015

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.

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
8c913f2 = "%System Root%\8c913f23\8c913f23.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
8c913f23 = "%User Profile%\Application Data\8c913f23.exe"

Other System Modifications

This Trojan deletes the following files:

  • %System Root%\8c913f23

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

It adds the following registry keys:

HKEY_CURRENT_USER\software\6CEFE75C6EBC1E00DBDD403B784F7A8A

HKEY_CURRENT_USER\software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF

It adds the following registry entries:

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A
ek = "{random values}"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A
fu = "{random characters}"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A
er = "{random characters}"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A
7v = "{random characters}"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Internet Explorer\brndlog.bak = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Internet Explorer\brndlog.txt = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%Application Data%\Microsoft\Windows Media\9.0\WMSDKNS.DTD = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Templates\excel.xls = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Templates\excel4.xls = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Templates\powerpnt.ppt = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Templates\quattro.wb2 = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Templates\sndrec.wav = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Templates\winword.doc = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Templates\winword2.doc = "68adfd"

HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\
03447788AABBDDDF
%User Profile%\Templates\wordpfct.wpd = "68adfd"

It modifies the following registry entries:

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

Dropping Routine

This Trojan drops the following files:

  • %System Root%\8c913f23\8c913f23.exe
  • %User Profile%\Application Data\8c913f23.exe
  • %User Startup%\8c913f23.exe
  • A:\HELP_DECRYPT.TXT
  • A:\HELP_DECRYPT.HTML
  • A:\HELP_DECRYPT.URL
  • A:\HELP_DECRYPT.PNG
  • %User Profile%\Internet Explorer\brndlog.bak.q76
  • %User Profile%\Internet Explorer\brndlog.txt.j2i
  • %User Profile%\Internet Explorer\HELP_DECRYPT.TXT
  • %User Profile%\Internet Explorer\HELP_DECRYPT.HTML
  • %User Profile%\Internet Explorer\HELP_DECRYPT.URL
  • %User Profile%\Internet Explorer\HELP_DECRYPT.PNG
  • %User Profile%\Microsoft\HELP_DECRYPT.TXT
  • %User Profile%\Microsoft\HELP_DECRYPT.HTML
  • %User Profile%\Microsoft\HELP_DECRYPT.URL
  • %User Profile%\Microsoft\HELP_DECRYPT.PNG
  • %User Profile%\Application Data\HELP_DECRYPT.TXT
  • %User Profile%\Application Data\HELP_DECRYPT.HTML
  • %User Profile%\Application Data\HELP_DECRYPT.URL
  • %User Profile%\Application Data\HELP_DECRYPT.PNG
  • %Application Data%\Microsoft\Windows Media\9.0\WMSDKNS.DTD.g1t
  • %Application Data%\Microsoft\Windows Media\9.0\HELP_DECRYPT.TXT
  • %Application Data%\Microsoft\Windows Media\9.0\HELP_DECRYPT.HTML
  • %Application Data%\Microsoft\Windows Media\9.0\HELP_DECRYPT.URL
  • %Application Data%\Microsoft\Windows Media\9.0\HELP_DECRYPT.PNG
  • %Application Data%\Microsoft\Windows Media\HELP_DECRYPT.TXT
  • %Application Data%\Microsoft\Windows Media\HELP_DECRYPT.HTML
  • %Application Data%\Microsoft\Windows Media\HELP_DECRYPT.URL
  • %Application Data%\Microsoft\Windows Media\HELP_DECRYPT.PNG
  • %Application Data%\Microsoft\HELP_DECRYPT.TXT
  • %Application Data%\Microsoft\HELP_DECRYPT.HTML
  • %Application Data%\Microsoft\HELP_DECRYPT.URL
  • %Application Data%\Microsoft\HELP_DECRYPT.PNG
  • %Application Data%\HELP_DECRYPT.TXT
  • %Application Data%\HELP_DECRYPT.HTML
  • %Application Data%\HELP_DECRYPT.URL
  • %Application Data%\HELP_DECRYPT.PNG
  • %User Profile%\Local Settings\HELP_DECRYPT.TXT
  • %User Profile%\Local Settings\HELP_DECRYPT.HTML
  • %User Profile%\Local Settings\HELP_DECRYPT.URL
  • %User Profile%\Local Settings\HELP_DECRYPT.PNG
  • %User Profile%\Templates\excel.xls.v8w
  • %User Profile%\Templates\excel4.xls.b36
  • %User Profile%\Templates\powerpnt.ppt.4yt
  • %User Profile%\Templates\quattro.wb2.m58
  • %User Profile%\Templates\sndrec.wav.p0z
  • %User Profile%\Templates\winword.doc.tg0
  • %User Profile%\Templates\winword2.doc.o21
  • %User Profile%\Templates\wordpfct.wpd.wd6
  • %User Profile%\Templates\HELP_DECRYPT.TXT
  • %User Profile%\Templates\HELP_DECRYPT.HTML
  • %User Profile%\Templates\HELP_DECRYPT.URL
  • %User Profile%\Templates\HELP_DECRYPT.PNG
  • %User Profile%\HELP_DECRYPT.TXT
  • %User Profile%\HELP_DECRYPT.HTML
  • %User Profile%\HELP_DECRYPT.URL
  • %User Profile%\HELP_DECRYPT.PNG
  • %User Profile%\Internet Explorer\brndlog.bak.2c3
  • %User Profile%\Internet Explorer\brndlog.txt.5lv
  • %Application Data%\Microsoft\Windows Media\9.0\WMSDKNS.DTD.h2e
  • %User Profile%\Templates\excel.xls.d5a
  • %User Profile%\Templates\excel4.xls.x0b
  • %User Profile%\Templates\powerpnt.ppt.6qv
  • %User Profile%\Templates\quattro.wb2.k0z
  • %User Profile%\Templates\sndrec.wav.jd6
  • %User Profile%\Templates\winword.doc.k1a
  • %User Profile%\Templates\winword2.doc.794
  • %User Profile%\Templates\wordpfct.wpd.1l1
  • %System Root%\Documents and Settings\HELP_DECRYPT.TXT
  • %System Root%\Documents and Settings\HELP_DECRYPT.HTML
  • %System Root%\Documents and Settings\HELP_DECRYPT.URL
  • %System Root%\Documents and Settings\HELP_DECRYPT.PNG
  • %System Root%\HELP_DECRYPT.TXT
  • %System Root%\HELP_DECRYPT.HTML
  • %System Root%\HELP_DECRYPT.URL
  • %System Root%\HELP_DECRYPT.PNG
  • %Desktop%\HELP_DECRYPT.TXT
  • %Desktop%\HELP_DECRYPT.HTML
  • %Desktop%\HELP_DECRYPT.URL
  • %Desktop%\HELP_DECRYPT.PNG
  • %User Startup%\HELP_DECRYPT.TXT
  • %User Startup%\HELP_DECRYPT.HTML
  • %User Startup%\HELP_DECRYPT.URL
  • %User Startup%\HELP_DECRYPT.PNG

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %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.. %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.. %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.. %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}r.es
  • http://{BLOCKED}nt.com
  • {BLOCKED}5.164.184
  • {BLOCKED}5.120.19
  • {BLOCKED}.216.31

It deletes itself after execution.

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.750

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

Restart in Safe Mode

[ Learn More ]

Step 3

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
    • 6CEFE75C6EBC1E00DBDD403B784F7A8A
  • In HKEY_CURRENT_USER\software\6CEFE75C6EBC1E00DBDD403B784F7A8A
    • 03447788AABBDDDF

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
    • 8c913f2 = "%System Root%\8c913f23\8c913f23.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • 8c913f23 = "%User Profile%\Application Data\8c913f23.exe"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A
    • ek = "{random values}"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A
    • fu = "{random characters}"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A
    • er = "{random characters}"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A
    • 7v = "{random characters}"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Internet Explorer\brndlog.bak = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Internet Explorer\brndlog.txt = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %Application Data%\Microsoft\Windows Media\9.0\WMSDKNS.DTD = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Templates\excel.xls = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Templates\excel4.xls = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Templates\powerpnt.ppt = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Templates\quattro.wb2 = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Templates\sndrec.wav = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Templates\winword.doc = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Templates\winword2.doc = "68adfd"
  • In HKEY_CURRENT_USER\Software\6CEFE75C6EBC1E00DBDD403B784F7A8A\03447788AABBDDDF
    • %User Profile%\Templates\wordpfct.wpd = "68adfd"

Step 5

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

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

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.
  • %System Root%\8c913f23\8c913f23.exe
  • %User Profile%\Application Data\8c913f23.exe
  • %User Startup%\8c913f23.exe
  • A:\HELP_DECRYPT.TXT
  • A:\HELP_DECRYPT.HTML
  • A:\HELP_DECRYPT.URL
  • A:\HELP_DECRYPT.PNG
  • %User Profile%\Internet Explorer\brndlog.bak.q76
  • %User Profile%\Internet Explorer\brndlog.txt.j2i
  • %User Profile%\Internet Explorer\HELP_DECRYPT.TXT
  • %User Profile%\Internet Explorer\HELP_DECRYPT.HTML
  • %User Profile%\Internet Explorer\HELP_DECRYPT.URL
  • %User Profile%\Internet Explorer\HELP_DECRYPT.PNG
  • %User Profile%\Microsoft\HELP_DECRYPT.TXT
  • %User Profile%\Microsoft\HELP_DECRYPT.HTML
  • %User Profile%\Microsoft\HELP_DECRYPT.URL
  • %User Profile%\Microsoft\HELP_DECRYPT.PNG
  • %User Profile%\Application Data\HELP_DECRYPT.TXT
  • %User Profile%\Application Data\HELP_DECRYPT.HTML
  • %User Profile%\Application Data\HELP_DECRYPT.URL
  • %User Profile%\Application Data\HELP_DECRYPT.PNG
  • %Application Data%\Microsoft\Windows Media\9.0\WMSDKNS.DTD.g1t
  • %Application Data%\Microsoft\Windows Media\9.0\HELP_DECRYPT.TXT
  • %Application Data%\Microsoft\Windows Media\9.0\HELP_DECRYPT.HTML
  • %Application Data%\Microsoft\Windows Media\9.0\HELP_DECRYPT.URL
  • %Application Data%\Microsoft\Windows Media\9.0\HELP_DECRYPT.PNG
  • %Application Data%\Microsoft\Windows Media\HELP_DECRYPT.TXT
  • %Application Data%\Microsoft\Windows Media\HELP_DECRYPT.HTML
  • %Application Data%\Microsoft\Windows Media\HELP_DECRYPT.URL
  • %Application Data%\Microsoft\Windows Media\HELP_DECRYPT.PNG
  • %Application Data%\Microsoft\HELP_DECRYPT.TXT
  • %Application Data%\Microsoft\HELP_DECRYPT.HTML
  • %Application Data%\Microsoft\HELP_DECRYPT.URL
  • %Application Data%\Microsoft\HELP_DECRYPT.PNG
  • %Application Data%\HELP_DECRYPT.TXT
  • %Application Data%\HELP_DECRYPT.HTML
  • %Application Data%\HELP_DECRYPT.URL
  • %Application Data%\HELP_DECRYPT.PNG
  • %User Profile%\Local Settings\HELP_DECRYPT.TXT
  • %User Profile%\Local Settings\HELP_DECRYPT.HTML
  • %User Profile%\Local Settings\HELP_DECRYPT.URL
  • %User Profile%\Local Settings\HELP_DECRYPT.PNG
  • %User Profile%\Templates\excel.xls.v8w
  • %User Profile%\Templates\excel4.xls.b36
  • %User Profile%\Templates\powerpnt.ppt.4yt
  • %User Profile%\Templates\quattro.wb2.m58
  • %User Profile%\Templates\sndrec.wav.p0z
  • %User Profile%\Templates\winword.doc.tg0
  • %User Profile%\Templates\winword2.doc.o21
  • %User Profile%\Templates\wordpfct.wpd.wd6
  • %User Profile%\Templates\HELP_DECRYPT.TXT
  • %User Profile%\Templates\HELP_DECRYPT.HTML
  • %User Profile%\Templates\HELP_DECRYPT.URL
  • %User Profile%\Templates\HELP_DECRYPT.PNG
  • %User Profile%\HELP_DECRYPT.TXT
  • %User Profile%\HELP_DECRYPT.HTML
  • %User Profile%\HELP_DECRYPT.URL
  • %User Profile%\HELP_DECRYPT.PNG
  • %User Profile%\Internet Explorer\brndlog.bak.2c3
  • %User Profile%\Internet Explorer\brndlog.txt.5lv
  • %Application Data%\Microsoft\Windows Media\9.0\WMSDKNS.DTD.h2e
  • %User Profile%\Templates\excel.xls.d5a
  • %User Profile%\Templates\excel4.xls.x0b
  • %User Profile%\Templates\powerpnt.ppt.6qv
  • %User Profile%\Templates\quattro.wb2.k0z
  • %User Profile%\Templates\sndrec.wav.jd6
  • %User Profile%\Templates\winword.doc.k1a
  • %User Profile%\Templates\winword2.doc.794
  • %User Profile%\Templates\wordpfct.wpd.1l1
  • %System Root%\Documents and Settings\HELP_DECRYPT.TXT
  • %System Root%\Documents and Settings\HELP_DECRYPT.HTML
  • %System Root%\Documents and Settings\HELP_DECRYPT.URL
  • %System Root%\Documents and Settings\HELP_DECRYPT.PNG
  • %System Root%\HELP_DECRYPT.TXT
  • %System Root%\HELP_DECRYPT.HTML
  • %System Root%\HELP_DECRYPT.URL
  • %System Root%\HELP_DECRYPT.PNG
  • %Desktop%\HELP_DECRYPT.TXT
  • %Desktop%\HELP_DECRYPT.HTML
  • %Desktop%\HELP_DECRYPT.URL
  • %Desktop%\HELP_DECRYPT.PNG
  • %User Startup%\HELP_DECRYPT.TXT
  • %User Startup%\HELP_DECRYPT.HTML
  • %User Startup%\HELP_DECRYPT.URL
  • %User Startup%\HELP_DECRYPT.PNG

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_CRYPWALL.YK. 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 this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %System Root%\8c913f23


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