BKDR_PRORAT.SL

 Analysis by: Sabrina Lei Sioting

 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


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 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:

1,590,316 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

17 Nov 2009

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 copies of itself into the affected system:

  • %Windows%\services.exe
  • %Windows%\system\sservice.exe
  • %System%\fservice.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.. %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 files:

  • %System%\reginv.dll
  • %System%\winkey.dll
  • %System%\drivers\oreans32.sys

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run
DirectX For Microsoft® Windows = "%System%\fservice.exe"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "Explorer.exe %System%\fservice.exe"

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

Other System Modifications

This backdoor deletes the following files:

  • %System%\Restore\MachineGuid.txt

(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 adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
Bulas = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
FW_KILL = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
XP_FW_Disable = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
XP_SYS_Recovery = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
ICQ_UIN = "084/41/051/069"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
Kurban_Ismi = "whbuhl"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
Mail = "`cs`i`ljdsoAinul`hm/ed"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
Online_List = ""

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
Port = "4001"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
Sifre = "032547"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
Hata = ""

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
KSil = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{5Y99AE78-58TT-11dW-BE53-Y67078979Y}
StubPath = "%Windows%\system\sservice.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
ICQ_UIN2 = "290446520"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
LanNotifie = ""

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
Tport = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
ServerVersionInt = "19"

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SystemRestore
DisableSR = "1"

(Note: The default value data of the said registry entry is 0.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\sr
Start = "4"

(Note: The default value data of the said registry entry is 0.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\sr\Parameters
FirstRun = "1"

(Note: The default value data of the said registry entry is 0.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\srservice
Start = "4"

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

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{5Y99AE78-58TT-11dW-BE53-Y67078979Y}

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.

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

6.668.04

FIRST VSAPI PATTERN DATE:

03 Dec 2009

VSAPI OPR PATTERN File:

6.669.00

VSAPI OPR PATTERN Date:

04 Dec 2009

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

Identify and delete files detected as BKDR_PRORAT.SL using either the Startup Disk or Recovery Console

[ Learn More ]

Step 3

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_CURRENT_USER\Software\Microsoft
    • Windows NT Script Host
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components
    • {5Y99AE78-58TT-11dW-BE53-Y67078979Y}

Step 4

Delete this 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\CurrentVersion\policies\Explorer\Run
    • DirectX For Microsoft® Windows = "%System%\fservice.exe"

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\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SystemRestore
    • From: DisableSR = "1"
      To: DisableSR = 0
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Shell = "Explorer.exe %System%\fservice.exe"
      To: Shell = "Explorer.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\sr
    • From: Start = "4"
      To: Start = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\sr\Parameters
    • From: FirstRun = "1"
      To: FirstRun = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\srservice
    • From: Start = "4"
      To: Start = 2

Step 6

Search and delete this file

[ 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.
  • %System%\reginv.dll
  • %System%\winkey.dll
  • %System%\drivers\oreans32.sys

Step 7

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

Step 8

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %System%\Restore\MachineGuid.txt


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