TROJ_FARFLI.XLS

October 09, 2012
 Analysis by: Karl Dominguez
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan arrives by being dropped by a specific malware. It modifies the affected system's registry in order to execute the malware it drops as a service.

This Trojan may be dropped by other malware.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size:

65,024 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

21 May 2011

Payload:

Drops files, Terminates processes

Arrival Details

This Trojan may be dropped by the following malware:

  • TROJ_XDROP.XLS

Installation

This Trojan drops the following files:

  • %System%\{Service name}ex.dll - BKDR_FARFLI.XLS

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

Autostart Technique

This Trojan creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{found service name}
Type = "120"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{found service name}
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{found service name}
ErrorControl = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{found service name}
DisplayName = "{found service name}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{found service name}
Description = Manages audio devices for Windows-based programs. If this service is stopped, audio devices and effects will not function properly. If this service is disabled, any services that explicitly depend on it will fail to start.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{found service name}\Parameters
ServiceDll = "%System%\{malware filename}ex.dll"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{found service name}\Security
Security = "{hex values}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{found service name}
ImagePath = "%System%\svchost.exe -k netsvcs"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{found service name}
ObjectName = "LocalSystem"

Process Termination

This Trojan terminates the following processes if found running in the affected system's memory:

  • avp.exe
  • SfCtlCom.exe
  • ccsvchst.exe

Other Details

This Trojan deletes itself after execution.

NOTES:
It parses the following registry entry to determine Network Services names:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Svchost netsvc

If the malware finds any Network Service that has no System Service, it will use the found name as file name for its dropped malware and the malware's service. By doing this, the dropped malware executes as a service every time the affected system is started.

  SOLUTION

Minimum Scan Engine:

8.900

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Remove malware files dropped/downloaded by TROJ_FARFLI.XLS

    • TROJ_XDROP.XLS
    • BKDR_FARFLI.XLS

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • {found service name}

Step 4

Scan your computer with your Trend Micro product to delete files detected as TROJ_FARFLI.XLS. 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:
To identify the service name used by the malware, please scan your computer with your Trend Micro product and note the name of the file detected as BKDR_FARFLI.XLS.


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