Analysis by: Anthony Joe Melgarejo
ALIASES:

Tepfer.3232 (ClamAV)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It employs registry shell spawning by adding certain registry entries. This allows this malware to execute even when other applications are opened.

  TECHNICAL DETAILS

File Size: 73,728 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 21 May 2013

Arrival Details

This backdoor 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 backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{C9835C0F-0B89-CE8E-8164-753D8B3C9060}
StubPath = "%Windows%:mswinchite.exe"

It employs registry shell spawning to ensure its execution when certain file types are accessed by adding the following entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
My20130401.Document\shell\open\
command
Default = "{malware path and file name} /dde"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
My20130401.Document\shell\open\
ddeexec
Default = "[open("%1")]"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
My20130401.Document\shell\print\
command
Default = "{malware path and file name} /dde"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
My20130401.Document\shell\print\
ddeexec
Default = "[print("%1")]"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
My20130401.Document\shell\printto\
command
Default = "{malware path and file name} /dde"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
My20130401.Document\shell\printto\
ddeexec
Default = "[printto("%1","%2","%3","%4")]"

Other System Modifications

This backdoor adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
My20130401.Document
Default = "My2013 Document"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
My20130401.Document\DefaultIcon
Default = "{malware path and file name},1"

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

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
My20130401.Document

HKEY_CURRENT_USER\Software\Local AppWizard-Generated Applications\
20130401

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://{BLOCKED}s.{BLOCKED}wen.com

NOTES:

It drops a copy of itself to an alternate data stream (ADS) and saves it as %Windows%:mswinchite.exe.

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 9.934.02
FIRST VSAPI PATTERN DATE: 22 May 2013
VSAPI OPR PATTERN File: 9.935.00
VSAPI OPR PATTERN Date: 23 May 2013

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

Identify and terminate files detected as BKDR_POISON.EUC

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 3

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\{C9835C0F-0B89-CE8E-8164-753D8B3C9060}
    • StubPath = "%Windows%:mswinchite.exe"

Step 4

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Classes
    • My20130401.Document
  • In HKEY_CURRENT_USER\Software\Local AppWizard-Generated Applications
    • 20130401

Step 5

Scan your computer with your Trend Micro product to delete files detected as BKDR_POISON.EUC. 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.

NOTES:

Before proceeding to Step 5, Remove added Alternate Data Streams:

  • Download Streams.exe.

Extract the contents of this file to a location of your choice. Open a command prompt window. Click Start > Run.

  • On Windows 98 and ME, type COMMAND, then press Enter.
  • On Windows NT, 2000, XP, and Server 2003, type CMD, then press Enter.

In the command prompt, type the following, then press Enter:

  • CD {Path where contents of downloaded file was extracted}

Still in the command prompt type the following then press Enter:

  • Streams.exe -d %windir%

Type exit then press enter.


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