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BKDR_FEXEL.SM1

October 10, 2013
 Analysis by: Alvin Bacani
 ALIASES:

Backdoor:Win32/Fexel.A (Microsoft); Backdoor.Fexel (Symantec)

 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:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware


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 deletes itself after execution.

  TECHNICAL DETAILS

File Size:

26,112 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

19 Sep 2013

Payload:

Compromises system security

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.

Installation

This backdoor drops the following component file(s):

  • %All User Profile%\Application Data\{variable filename}.dll - detected as BKDR_FEXEL.SM2

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{variable filename} = "rundll32.exe %All User Profile%\Application Data\{variable filename}.dll,Launch"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
{variable filename} = "rundll32.exe %All User Profile%\Application Data\{variable filename}.dll,Launch"

Other Details

This backdoor deletes itself after execution.

NOTES:
The malware then executes the dropped component file which contains the main backdoor routine.

  SOLUTION

Minimum Scan Engine:

9.300

VSAPI OPR PATTERN File:

10.289.00

VSAPI OPR PATTERN Date:

19 Sep 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

Restart in Safe Mode

[ Learn More ]

Step 3

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.  
  • %All User Profile%\Application Data\{variable filename}.dll

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
    • {variable filename} = "rundll32.exe %All User Profile%\Application Data\{variable filename}.dll,Launch"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • {variable filename} = "rundll32.exe %All User Profile%\Application Data\{variable filename}.dll,Launch"

Step 5

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_FEXEL.SM1. 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.


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