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: No

  • In the wild: Yes

  OVERVIEW

This backdoor may be dropped by other malware.

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.

  TECHNICAL DETAILS

File Size: Varies
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 01 Jul 2011
Payload: Drops files, Compromises system security, Connects to URLs/IPs

Arrival Details

This backdoor may be dropped by the following malware:

  • TROJ_PIDIEF.CSW
  • TROJ_PIDIEF.CSX
  • TROJ_PIDIEF.CRW

Installation

This backdoor drops the following component file(s):

  • %System%\strunlib.dll - also detected as BKDR_TROGBOT.A

(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 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\MSStorage\Parameters
ServiceDll = strunlib.dll

Other System Modifications

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Storage\STConfig

Backdoor Routine

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

  • Download Files
  • Upload Files
  • Manage Files
  • Execute Files
  • Check Drives
  • Send Message
  • Hibernate affected Machine

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

  • {BLOCKED}4.{BLOCKED}3.248.70
  • {BLOCKED}9.{BLOCKED}2.148.82

  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 BKDR_TROGBOT.A

    • TROJ_PIDIEF.CSW
    • TROJ_PIDIEF.CSX
    • TROJ_PIDIEF.CRW

Step 3

Restart in Safe Mode

[ Learn More ]

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\Microsoft\Storage
    • STConfig
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • MSStorage

Step 5

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