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BKDR_SMALLDOO.AQ

October 16, 2012
 ALIASES:

Backdoor:Win32/Prorat.T (Microsoft); BackDoor-AVW (McAfee); Backdoor.Prorat (Symantec); PAK:ASPack, PAK:UPX, Backdoor.Win32.VB.aoi, Backdoor.Win32.Prorat.oek (Kaspersky); BehavesLike.Win32.Malware.ssc (mx-v) (Sunbelt)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • 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.

  TECHNICAL DETAILS

File Size:

323,116 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

16 Oct 2012

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:

  • %System%\fservice.exe
  • %System%\sservice.exe

(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\
Active Setup\Installed Components\{5Y99AE78-58TT-11dW-BE53-Y67078979Y}
StubPath = "%System%\sservice.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%\sservice.exe
  • %Windows%\Pplugin4.exe
  • %Windows%\Pplugin8.exe
  • %Windows%\Pplugin10xa.exe
  • %Windows%\eimsn.exe
  • %Windows%\winp9.exe
  • %Windows%\PpluginCd.dll

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

It adds the following registry keys:

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run

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

It adds the following registry entries:

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
Kurban_Ismi = "whuuhl`"

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 = "pvd@RE0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT Script Host\Microsoft DxDiag\WinSettings
Hata = "Invalid memory block address"

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

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

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 entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\srservice
Start = "4"

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

It deletes the following registry keys:

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

Dropping Routine

This backdoor drops the following files:

  • %System%\winkey.dll
  • %System%\reginv.dll
  • %Windows%\services.exe
  • %System%\fservice.exe
  • %System%\sservice.exe

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

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.200

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_SMALLDOO.AQ 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.

  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows NT Script Host\Microsoft DxDiag
    • WinSettings
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Explorer
    • Run
  • 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\Active Setup\Installed Components\{5Y99AE78-58TT-11dW-BE53-Y67078979Y}
    • StubPath = "%System%\sservice.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • Bulas = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • FW_KILL = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • XP_FW_Disable = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • XP_SYS_Recovery = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • Kurban_Ismi = "whuuhl`"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • Port = "4001"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • Sifre = "pvd@RE0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • Hata = "Invalid memory block address"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • KSil = "1"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Explorer\Run
    • DirectX For Microsoft® Windows = "%System%\fservice.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • Tport = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT Script Host\Microsoft DxDiag\WinSettings
    • ServerVersionInt = "19"

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\ControlSet001\Services\srservice
    • From: Start = "4"
      To: Start = ""2""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Shell = "Explorer.exe %System%\fservice.exe"
      To: Shell = ""Explorer.exe""

Step 6

Search and delete these files

[ 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%\winkey.dll
  • %System%\reginv.dll
  • %Windows%\services.exe
  • %System%\fservice.exe
  • %System%\sservice.exe

Step 7

Scan your computer with your Trend Micro product to delete files detected as BKDR_SMALLDOO.AQ. 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%\sservice.exe
  • %Windows%\Pplugin4.exe
  • %Windows%\Pplugin8.exe
  • %Windows%\Pplugin10xa.exe
  • %Windows%\eimsn.exe
  • %Windows%\winp9.exe
  • %Windows%\PpluginCd.dll

Step 9

Restore these deleted registry keys/values from backup

*Note: Only Microsoft-related keys/values will be restored. If the malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.

  • In HKEY_CURRENT_USER\Software\Microsoft\Active Setup\Installed Components
    • {5Y99AE78-58TT-11dW-BE53-Y67078979Y}


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