WORM_SOHANAD.UN
Windows 2000, Windows XP, Windows Server 2003
Threat Type: Worm
Destructiveness: No
Encrypted:
In the wild: Yes
OVERVIEW
This worm arrives by connecting affected removable drives to a system. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
It uses the Windows Task Scheduler to add a scheduled task that executes the copies it drops.
It disables Task Manager, Registry Editor, and Folder Options.
It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.
TECHNICAL DETAILS
Arrival Details
This worm arrives by connecting affected removable drives to a system.
It 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 drops the following copies of itself into the affected system:
- %Windows%\SSCVIHOST.exe
- %System%\blastclnnn.exe
- %System%\SSCVIHOST.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 file(s)/component(s):
- %System%\autorun.ini
- %Windows%\Tasks\At1.job
(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 uses the Windows Task Scheduler to add a scheduled task that executes the copies it drops.
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
Yahoo Messengger = "%System%\SSCVIHOST.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 SSCVIHOST.exe"
(Note: The default value data of the said registry entry is "Explorer.exe".)
The scheduled task executes the malware every:
- 9:00 am
Other System Modifications
This worm adds the following registry entries as part of its installation routine:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Schedule
AtTaskMaxHours = "0"
It modifies the following registry entries:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Schedule
NextAtJobId = "2"
(Note: The default value data of the said registry entry is 1.)
It creates the following registry entry(ies) to disable Task Manager, Registry Tools and Folder Options:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = "1"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = "1"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Explorer
NofolderOptions = "1"
Propagation
This worm drops the following copy(ies) of itself in all removable drives:
- New Folder.exe
- SSCVIHOST.exe
It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.
The said .INF file contains the following strings:
[Autorun]
Open=SSCVIHOST.exe
Shellexe cute=SSCVIHOST.exe
Shell\Open\command=SSCVIHOST.exe
Shell=Open
SOLUTION
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 terminate files detected as WORM_SOHANAD.UN
- If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
- If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.
Step 3
Enable Registry Editor, Task Manager, and Folder options
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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
- Yahoo Messengger = %System%\SSCVIHOST.exe
- Yahoo Messengger = %System%\SSCVIHOST.exe
- In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Schedule
- AtTaskMaxHours = 0
- AtTaskMaxHours = 0
Step 5
Restore this modified 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\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
- From: Shell = Explorer.exe SSCVIHOST.exe
To: Shell = Explorer.exe
- From: Shell = Explorer.exe SSCVIHOST.exe
- In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Schedule
- From: NextAtJobId = 2
To: NextAtJobId = 1
- From: NextAtJobId = 2
Step 6
Search and delete these files
- %System%\autorun.ini
- %Windows%\Tasks\At1.job
Step 7
Search and delete AUTORUN.INF files created by WORM_SOHANAD.UN that contain these strings
Step 8
Scan your computer with your Trend Micro product to delete files detected as WORM_SOHANAD.UN. 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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