BKDR_FARFLI.AAN

October 09, 2012
 Analysis by: Michael Cabel
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 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.

  TECHNICAL DETAILS

File Size:

65,536 bytes

File Type:

DLL

Memory Resident:

Yes

Initial Samples Received Date:

18 Apr 2011

Payload:

Connects to URLs/IPs

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):

  • %Program Files%\Tkka\Hccexkxav.jpg - also detected as BKDR_FARFLI.AAN

(Note: %Program Files% is the default Program Files folder, usually C:\Program Files.)

It injects itself into the following processes as part of its memory residency routine:

  • svchost.exe

Autostart Technique

This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Estxnn Jhyrmbot Gkr\Parameters
ServiceDll = "%Program Files%\Tkka\Hccexkxav.jpg"

HKEY_LOCAL_MACHINE\SOFTWARE\{Random Key 1}\
Parameters
ServiceDll = "%Program Files%\Tkka\Hccexkxav.jpg"

HKEY_LOCAL_MACHINE\SOFTWARE\{Random Key 2}\
Parameters
ServiceDll = "%Program Files%\Tkka\Hccexkxav.jpg"

HKEY_LOCAL_MACHINE\SOFTWARE\{Random Key 3}\
Parameters
ServiceDll = "%Program Files%\Tkka\Hccexkxav.jpg"

Other System Modifications

This backdoor modifies the following registry key(s)/entry(ies) as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
imgsvc = "StiSvc Estxnn Jhyrmbot Gkr"

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

Backdoor Routine

This backdoor opens the following port(s) where it listens for remote commands:

  • TCP 9999

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • {BLOCKED}9418.3322.org

As of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

7.984.05

FIRST VSAPI PATTERN DATE:

18 Apr 2011

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

Restart in Safe Mode

[ Learn More ]

Step 3

To delete the random service key this malware/grayware created:

  1. Scan your computer with your Trend Micro product and take note of the name of the malware/grayware/spyware detected.
  2. Open Registry Editor. To do this, click Start>Run, type regedit in the text box provided, then press Enter.
  3. Press CTRL+F.
  4. In the Find dialog box, type the file name of the malware detected earlier.
    (Note: Make sure that only the data checkbox is selected, then click Find Next.)

    5. Find.

  5. Once found, in the right panel, check if the result is the following value-data pair:
    ImagePath = {malware/grayware path and file name}
  6. If yes, in the left panel, locate the service where the data is under.
  7. Right-click on the located service in the left panel and choose Delete.
  8. Repeat steps 2 to 6 until the Finished searching through the registry dialog box appears.
  9. Close Registry Editor.

Step 4

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\SvcHost
    • From: imgsvc = StiSvc Estxnn Jhyrmbot Gkr
      To: StiSvc

Step 5

Search and delete these files

[ Learn More ]
There may be some component 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.
  • %Program Files%\Tkka\Hccexkxav.jpg

Step 6

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