Worm.Win32.MEREDROP.AA
W32.Pilleuz (NORTON)
Windows
Threat Type: Worm
Destructiveness: No
Encrypted:
In the wild: Yes
OVERVIEW
This Worm 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
Arrival Details
This Worm 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 Worm adds the following folders:
- {Drive}\driver
- {Drive}\driver\info
It drops the following files:
- %User Temp%\remove.bat → deleted afterwards
- {Drive}\driver\info\Desktop.ini
- {Drive}\autorun.inf
(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(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)
It drops the following copies of itself into the affected system:
- %User Temp%\csrssa.exe
- {Drive}\driver\info\csrssa.exe
(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(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)
It adds the following processes:
- cmd /c "%User Temp%\remove.bat"
- %User Temp%\csrssa.exe
(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(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)
Autostart Technique
This Worm adds the following registry entries to enable its automatic execution at every system startup:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Microsoft Windows Hosting Service = %User Temp%\csrssa.exe
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Taskman = %User Temp%\csrssa.exe
Other System Modifications
This Worm adds the following registry entries:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
Zvpebfbsg Jvaqbjf Ubfgvat Freivpr = %User Temp%\csrssa.exe
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
Associations
DefaultFileTypeRisk = 808464432
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
Associations
LowRiskFileTypes = .exe
HKEY_CURRENT_USER\FBSGJNER\Zvpebfbsg\
Jvaqbjf AG\PheeragIrefvba\Jvaybtba
%User Temp%\csrssa.exe = %User Temp%\csrssa.exe
Adware Routine
This Worm deletes itself after execution.
Other Details
This Worm adds the following registry keys:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
Associations
HKEY_CURRENT_USER\FBSGJNER
HKEY_CURRENT_USER\FBSGJNER\Zvpebfbsg
HKEY_CURRENT_USER\FBSGJNER\Zvpebfbsg\
Jvaqbjf AG
HKEY_CURRENT_USER\FBSGJNER\Zvpebfbsg\
Jvaqbjf AG\PheeragIrefvba
HKEY_CURRENT_USER\FBSGJNER\Zvpebfbsg\
Jvaqbjf AG\PheeragIrefvba\Jvaybtba
SOLUTION
Step 1
Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 users must disable System Restore to allow full scanning of their computers.
Step 2
Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.
Step 3
Restart in Safe Mode
Step 4
Delete this registry value
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\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
- Zvpebfbsg Jvaqbjf Ubfgvat Freivpr = %User Temp%\csrssa.exe
- Zvpebfbsg Jvaqbjf Ubfgvat Freivpr = %User Temp%\csrssa.exe
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Associations
- DefaultFileTypeRisk = 808464432
- DefaultFileTypeRisk = 808464432
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Associations
- LowRiskFileTypes = .exe
- LowRiskFileTypes = .exe
- In HKEY_CURRENT_USER\FBSGJNER\Zvpebfbsg\Jvaqbjf AG\PheeragIrefvba\Jvaybtba
- %User Temp%\csrssa.exe = %User Temp%\csrssa.exe
- %User Temp%\csrssa.exe = %User Temp%\csrssa.exe
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
- Microsoft Windows Hosting Service = %User Temp%\csrssa.exe
- Microsoft Windows Hosting Service = %User Temp%\csrssa.exe
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
- Taskman = %User Temp%\csrssa.exe
- Taskman = %User Temp%\csrssa.exe
Step 5
Delete this registry key
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\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\
- List
- List
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\
- Associations
- Associations
- In HKEY_CURRENT_USER\
- FBSGJNER
- FBSGJNER
- In HKEY_CURRENT_USER\FBSGJNER\Zvpebfbsg\Jvaqbjf AG\PheeragIrefvba\
- Jvaybtba
- Jvaybtba
- In HKEY_CURRENT_USER\FBSGJNER\Zvpebfbsg\Jvaqbjf AG\
- PheeragIrefvba
- PheeragIrefvba
- In HKEY_CURRENT_USER\FBSGJNER\Zvpebfbsg\
- Jvaqbjf AG
- Jvaqbjf AG
- In HKEY_CURRENT_USER\FBSGJNER\
- Zvpebfbsg
- Zvpebfbsg
Step 6
Search and delete these files
- {Drive}\driver\info\Desktop.ini
- {Drive}\autorun.inf
- %User Temp%\csrssa.exe
- {Drive}\driver\info\csrssa.exe
Step 7
Search and delete this folder
- {Drive}\driver\info
- {Drive}\driver
Step 8
Restart in normal mode and scan your computer with your Trend Micro product for files detected as Worm.Win32.MEREDROP.AA. 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.
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