BKDR_AFCORE.DI

 Analysis by: kathleenno

 ALIASES:

Troj/Backdr-EX (Sophos)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

This backdoor monitors the browsing activities of the user and logs keystroke when the user is accessing sites with certain strings.

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 may be injected into processes running in memory.

It opens a random port to allow a remote user to connect to the affected system. Once a successful connection is established, the remote user executes commands on the affected system.

It requires its main component to successfully perform its intended routine.

  TECHNICAL DETAILS

File Size:

173,056 bytes

File Type:

DLL

Memory Resident:

Yes

Initial Samples Received Date:

01 Apr 2011

Payload:

Steals information

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 non-malicious files:

  • %System%\{random filename 1}.dat
  • %System%\{random filename 2}.dat
  • %System%\{random filename 3}.dat
  • %System%\{random filename 4}.dat
  • %Current%\{malware filename}.dat

(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.)

It drops the following copies of itself into the affected system:

  • %System%\{random filename 1}.ocx

(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.)

It may be injected into processes running in memory.

Autostart Technique

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

HKEY_CLASSES_ROOT\CLSID\{random CLSID}\
InprocServer32
(default} = {malware path and filename}

HKEY_CLASSES_ROOT\CLSID\{random CLSID}\
InprocServer32
(default) = %System%\{random filename 1}.ocx

Other System Modifications

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

HKEY_CLASSES_ROOT\CLSID\{random CLSID}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
ShellIconOverlayIdentifiers\{malware filename}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
ShellIconOverlayIdentifiers\{random filename 1}

Backdoor Routine

This backdoor opens a random port to allow a remote user to connect to the affected system. Once a successful connection is established, the remote user executes commands on the affected system.

Other Details

This backdoor requires its main component to successfully perform its intended routine.

NOTES:

It may perform the following actions:

  • Create, list, and delete cookies
  • Flood drives
  • Get IPC, log, and hook timeouts
  • Manipulate files
  • Obtain various system information (i.e., local time, drive information, idle time)
  • Perform distributed denial of service (DDoS) attack against a target site
  • Resolve host names
  • Respawn or uninstall itself
  • Restart Windows
  • Turn off the system

It monitors the following applications:

  • explorer.exe
  • iexplore.exe
  • firefox.exe
  • opera.exe
  • skype.exe

It also monitors the browsing activities of the user and logs keystroke when the user is accessing sites with the following strings:

  • *.nhs.net/*
  • *.nhs.uk/*
  • *.hilton.*
  • *.yahoo.*
  • *.google.*

  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

Scan your computer with your Trend Micro product and note files detected as BKDR_AFCORE.DI

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete the created random CLSID 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.

Step 5

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\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers
    • {malware filename}
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers
    • {random filename 1}

Step 6

Scan your computer with your Trend Micro product to delete files detected as BKDR_AFCORE.DI. 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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