BKDR_PROSTI.AA

Malware type: Backdoor

Aliases: Trojan Horse (Symantec), CC/00163 (Avira),

In the wild: Yes

Destructive: No

Language: English

Platform: Windows 98, ME, NT, 2000, XP, Server 2003

Encrypted: No

Overall risk rating:

Reported infections:

Damage potential:

High

Distribution potential:

Low

Infection Channel 1 : Spammed via email


Description: 

To get a one-glance comprehensive view of the behavior of this backdoor, refer to the Behavior Diagram shown below.

BKDR_PROSTI.AA Behavior Diagram

Malware Overview

This backdoor application arrives on a system either as a downloaded file from the Internet or as an attachment to an email message manually mass-mailed by a malicious user.

When executed, it drops several components in the hardcoded path, C:\WINDOWS\Media.

This backdoor application uses its backdoor component, LSASS.EXE, and opens port 6699 to wait for a remote malicious user to access and gain virtual control over the said system. This routine compromises system security and opens the affected machine to further attacks.

Its component, WINLOGON.EXE, allows a remote malicious user to use the affected system as a proxy server. Proxy servers act as an intermediary between a user and a server. A proxy usually listens on an open TCP port. When it receives an incoming request, it forwards the said request to the target server. Upon receiving a reply, the proxy server then forwards the received reply to the original user. This routine allows the remote malicious user's IP address to remain hidden while performing malicious routines. However, this backdoor needs the file, MSWINSCK.OCX, to properly execute the said routine.

Using its downloader component, ETHERNET.EXE, this backdoor waits for active Internet connection and accesses the following Web site to download and execute possibly malicious files on the affected system:

    http://winn{BLOCKED}to.org

As of this writing, however, the said Web site is unavailable.

For additional information about this threat, see:

Description created: May. 21, 2006 11:42:37 PM GMT -0800


TECHNICAL DETAILS


File type: PE

Memory resident:  Yes

Size of malware: Varies

Ports used: Port 6699 (Unassigned), Random

Initial samples received on: May 21, 2006

Payload 1: Downloads files

Details:

Arrival

This backdoor application arrives on a system either as a downloaded file from the Internet or as an attachment to an email message manually mass-mailed by a malicious user.

Installation and Autostart Techniques

When executed, this backdoor drops the following components in the hardcoded path, C:\WINDOWS\Media:

  • ethernet.exe
  • lsass.exe
  • winlogon.exe

It also drops the following non-malicious files in the hardcoded path, C:\WINDOWS\inf:

  • dllhost.exe
  • winf.exe

It then creates the following registry entries to ensure its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
DllHost = "C:\WINDOWS\inf\dllhost.exe"
msn = "C:\WINDOWS\Media\winlogon.exe"
SondBlaster = "C:\WINDOWS\Media\lsass.exe"
Yahoo! = "C:\WINDOWS\Media\ethernet.exe"

Backdoor Routine

This backdoor application uses its backdoor component, LSASS.EXE, and opens port 6699 to wait for a remote malicious user to access and gain virtual control over the said system. This routine compromises system security and opens the affected machine to further attacks.

Its component, WINLOGON.EXE, allows a remote malicious user to use the affected system as a proxy server. Proxy servers act as an intermediary between a user and a server. A proxy usually listens on an open TCP port. When it receives an incoming request, it forwards the said request to the target server. Upon receiving a reply, the proxy server then forwards the received reply to the original user. This routine allows the remote malicious user's IP address to remain hidden while performing malicious routines. However, this backdoor needs the file, MSWINSCK.OCX, to properly execute the said routine.

Download Routine

Using its downloader component, ETHERNET.EXE, this backdoor waits for active Internet connection and accesses the following Web site to download and execute possibly malicious files on the affected system:

    http://winn{BLOCKED}to.org

As of this writing, however, the said Web site is unavailable.

Affected Platforms

This backdoor runs on Windows 98, ME, NT, 2000, XP, and Server 2003.

Analysis By: Ronnie Giagone


SOLUTION


Minimum scan engine version needed: 7.500

Pattern file needed: 3.444.01

Pattern release date: May 22, 2006


Important note: The "Minimum scan engine" refers to the earliest Trend Micro scan engine version guaranteed to detect this threat. However, Trend Micro strongly recommends that you update to the latest version in order to get comprehensive protection. Download the latest scan engine here.

Solution:

Identifying the Malware Program

To remove this malware, first identify the malware program.

  1. Scan your computer with your Trend Micro antivirus product.
  2. NOTE the path and file name of all files detected as BKDR_PROSTI.AA.

Trend Micro customers need to download the latest virus pattern file before scanning their computer. Other users can use Housecall, the Trend Micro online virus scanner.

Terminating the Malware Program

This procedure terminates the running malware process. You will need the name(s) of the file(s) detected earlier.

If the process you are looking for is not in the list displayed by Task Manager, proceed to the succeeding solution set.

  1. Open Windows Task Manager.
    • On Windows 98 and ME, press
    CTRL%20ALT%20DELETE
    • On Windows NT, 2000, XP, and Server 2003, press
    CTRL%20SHIFT%20ESC, then click the Processes tab.
  2. In the list of running programs*, locate the malware file(s) detected earlier.
  3. Select one of the detected files, then press either the End Task or the End Process button, depending on the version of Windows on your computer.
  4. Do the same for all detected malware files in the list of running processes.
  5. To check if the malware process has been terminated, close Task Manager, and then open it again.
  6. Close Task Manager.

*NOTE: On computers running Windows 98 and ME, Windows Task Manager may not show certain processes. You can use a third party process viewer such as Process Explorer to terminate the malware process.

On computers running all Windows platforms, if the process you are looking for is not in the list displayed by Task Manager or Process Explorer, continue with the next solution procedure, noting additional instructions. If the malware process is in the list displayed by either Task Manager or Process Explorer, but you are unable to terminate it, restart your computer in safe mode.

Editing the Registry

This malware modifies the computer's registry. Users affected by this malware may need to modify or delete specific registry keys or entries. For detailed information regarding registry editing, please refer to the following articles from Microsoft:

  1. HOW TO: Backup, Edit, and Restore the Registry in Windows 95, Windows 98, and Windows ME
  2. HOW TO: Backup, Edit, and Restore the Registry in Windows NT 4.0
  3. HOW TO: Backup, Edit, and Restore the Registry in Windows 2000
  4. HOW TO: Back Up, Edit, and Restore the Registry in Windows XP and Server 2003

Removing Autostart Entries from the Registry

Removing autostart entries from the registry prevents the malware from executing at startup.

If the registry entries below are not found, the malware may not have executed as of detection. If so, proceed to the succeeding solution set.

  1. Open Registry Editor. Click Start>Run, type REGEDIT, then press Enter.
  2. In the left panel, double-click the following:
    HKEY_LOCAL_MACHINE>SOFTWARE>Microsoft>
    Windows>CurrentVersion>Run
  3. In the right panel, locate and delete the following entries:
    • DllHost = "C:\WINDOWS\inf\dllhost.exe"
    • msn = "C:\WINDOWS\Media\winlogon.exe"
    • SondBlaster = "C:\WINDOWS\Media\lsass.exe"
    • Yahoo! = "C:\WINDOWS\Media\ethernet.exe"
  4. Close Registry Editor.

Deleting the Malware Files

  1. Right-click Start then click Search... or Find..., depending on the version of Windows you are running.
  2. In the Named input box, type:
    C:\WINDOWS\inf\dllhost.exe
  3. In the Look In drop-down list, select the drive that contains Windows, then press Enter.
  4. Once located, select the file then press Delete.
  5. Repeat steps 2-4 for the following file:
    C:\WINDOWS\inf\winf.exe

Important Windows ME/XP Cleaning Instructions

Users running Windows ME and XP must disable System Restore to allow full scanning of infected computers.

Users running other Windows versions can proceed with the succeeding solution set(s).

Running Trend Micro Antivirus

If you are currently running in safe mode, please restart your computer normally before performing the following solution.

Scan your computer with Trend Micro antivirus and delete files detected as BKDR_PROSTI.AA. To do this, Trend Micro customers must download the latest virus pattern file and scan their computer. Other Internet users can use HouseCall, the Trend Micro online virus scanner.




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