Analysis by: Karl Dominguez
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

The malware dropper, detected as BKDR_REMOSH.SML is responsible for assigning what service name the malware will use by querying certain registry entry to enumerate network related services.

This backdoor may be dropped by other malware.

It modifies registry entries to disable various system services. This action prevents most of the system functions to be used.

It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size: Varies
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 27 May 2010
Payload: Compromises system security, Terminates processes

Arrival Details

This backdoor may be dropped by the following malware:

  • BKDR_REMOSH.SML

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\{Random Service Name}\Parameters
ServiceDLL = %System%\{malware file name}

Other System Modifications

This backdoor modifies registry entries to disable the following system services:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\PolicyAgent
Start = 4

(Note: The default value data of the said registry entry is 2.)

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Enumerate sessions to determine logged-in user
  • Enumerate files
  • Create and delete files
  • Send and receive files
  • Capture screenshots
  • Get drive information, such as type, free space, and name
  • Execute processes
  • Run remote command shell
  • Uninstall itself

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

  • {BLOCKED}l.is-a-chef.com
  • {BLOCKED}l.office-on-the.net
  • {BLOCKED}.{BLOCKED}.82.50
  • {BLOCKED}.{BLOCKED}.82.25

Process Termination

This backdoor terminates the following services if found on the affected system:

  • PolicyAgent

Other Details

This backdoor does the following:

  • Deletes the malware that originally dropped it
  • Creates services with the following details:

    DisplayName:
    • ASP.NET Service
    • Network Management
    • OfficeScan Support
    • Windows Network Station
    • ASP .NET Support
    Description:
    • Provides support for out-of-process session states for ASP.NET
    • Provides network installation services such as Assign, Publish, and Remove.
    • Enables Help and Support Center to run Officescan on this computer

  SOLUTION

Minimum Scan Engine: 8.900
VSAPI OPR PATTERN File: 7.777.00
VSAPI OPR PATTERN Date: 19 Jan 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

Remove malware files dropped/downloaded by BKDR_REMOSH.SMF

Step 3

Scan your computer with your Trend Micro product and note files detected as BKDR_REMOSH.SMF

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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\SYSTEM\CurrentControlSet\Services\PolicyAgent
    • From: Start = 4
      To: Start = 2

Step 6

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 7

Search and delete the file detected as BKDR_REMOSH.SMF

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files in the search result.

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_REMOSH.SMF. 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:
Note: In step 6, change the value of ImagePath = {Malware/Grayware/Spyware path and file name} to ServiceDLL = {Malware path and file name}


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