ALIASES:

ERROR (Sunbelt)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 163,840 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 17 May 2012

Arrival Details

This Trojan 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 Trojan drops the following copies of itself into the affected system:

  • %Windows%\S-1-5-21-3761900733-9855609303-097599164-0953\rundll.exe

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

It creates the following folders:

  • %Windows%\S-1-5-21-3761900733-9855609303-097599164-0953

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

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
csrrsss = "%User Profile%\Application Data\csrrsss.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Microsoft Windows Hosting Service = "%User Temp%\csrssr.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Microsoft Windows Hosting Service = "%User Temp%\csrssr.exe"

Other System Modifications

This Trojan deletes the following files:

  • %User Temp%\csrssr.exe
  • %User Profile%\rm.bat

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.. %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It adds the following registry keys:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\
Services\Run

HKEY_CURRENT_USER\System\CurrentControlSet\
Services\Run

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Policies\
Associations

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Run
Windows RPC Host Service = "%User Temp%\csrssr.exe"

HKEY_CURRENT_USER\System\CurrentControlSet\
Services\Run
Windows RPC Host Service = "%User Temp%\csrssr.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Microsoft Windows Firewall Service = "%User Temp%\csrssr.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
Microsoft Windows Firewall Service = "%User Temp%\csrssr.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Associations
DefaultFileTypeRisk = "3333"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Associations
LowRiskFileTypes = ".exe"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
Microsoft Windows Hosting Service = "%User Temp%\csrssr.exe"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
System = "%Windows%\S-1-5-21-3761900733-9855609303-097599164-0953\rundll.exe"

Dropping Routine

This Trojan drops the following files:

  • %Windows%\S-1-5-21-3761900733-9855609303-097599164-0953\Desktop.ini
  • %User Temp%\119.exe
  • %User Temp%\554.exe
  • %User Profile%\Application Data\csrrsss.exe
  • rm.bat
  • %User Temp%\csrssr.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.. %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.. %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}127.22/dl/winbmd.exe
  • http://{BLOCKED}127.22/dl/winmds.exe

It deletes itself after execution.

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

Restart in Safe Mode

[ 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_LOCAL_MACHINE\System\CurrentControlSet\Services\
    • Run
  • In HKEY_CURRENT_USER\System\CurrentControlSet\Services\
    • Run
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\
    • Associations

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • csrrsss = "%User Profile%\Application Data\csrrsss.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • Microsoft Windows Hosting Service = "%User Temp%\csrssr.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Microsoft Windows Hosting Service = "%User Temp%\csrssr.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Run
    • Windows RPC Host Service = "%User Temp%\csrssr.exe"
  • In HKEY_CURRENT_USER\System\CurrentControlSet\Services\Run
    • Windows RPC Host Service = "%User Temp%\csrssr.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Microsoft Windows Firewall Service = "%User Temp%\csrssr.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Microsoft Windows Firewall Service = "%User Temp%\csrssr.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Associations
    • DefaultFileTypeRisk = "3333"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Associations
    • LowRiskFileTypes = ".exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • Microsoft Windows Hosting Service = "%User Temp%\csrssr.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\Winlogon
    • System = "%Windows%\S-1-5-21-3761900733-9855609303-097599164-0953\rundll.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.
  • %Windows%\S-1-5-21-3761900733-9855609303-097599164-0953\Desktop.ini
  • %User Temp%\119.exe
  • %User Temp%\554.exe
  • %User Profile%\Application Data\csrrsss.exe
  • rm.bat
  • %User Temp%\csrssr.exe

Step 7

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Windows%\S-1-5-21-3761900733-9855609303-097599164-0953

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_MEREDROP.VN. 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 9

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.

  • %User Temp%\csrssr.exe
  • %User Profile%\rm.bat


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