TROJ_DROPPER.ZAS
TrojanDownloader:Win32/Thoper.D (Microsoft); Trojan horse Generic29.BDCL (AVG)
Windows 2000, Windows XP, Windows Server 2003
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
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.
Autostart Technique
This Trojan registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\
Services\mspool\Parameters
Other System Modifications
This Trojan adds the following registry entries:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\mspool\Parameters
ServiceDll = "%User Profile%\Application Data\mspool.DLL"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\mspool\Parameters
ServiceMain = "BofMrf"
It modifies the following registry entries:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
LocalService = "Alerter,WebClient,LmHosts,RemoteRegistry,upnphost,SSDPSRV,mspool"
(Note: The default value data of the said registry entry is {random values}.)
Dropping Routine
This Trojan drops the following files:
- %User Profile%\Application Data\mspool.DLL
(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)
Other Details
This Trojan connects to the following possibly malicious URL:
- http://mial.{BLOCKED}c.com/update?id=010c3d1c
- http://mial.{BLOCKED}c.com/update?id=7e51d894
- http://mial.{BLOCKED}c.com/update?id=b9f8e8e6
It deletes itself after execution.
This report is generated via an automated analysis system.
SOLUTION
Step 1
Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.
Step 2
Restart in Safe Mode
Step 3
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\CurrentControlSet\Services\mspool
- Parameters
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\mspool\Parameters
- ServiceDll = "%User Profile%\Application Data\mspool.DLL"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\mspool\Parameters
- ServiceMain = "BofMrf"
Step 5
Restore these modified registry values
Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SvcHost
- From: LocalService = "Alerter,WebClient,LmHosts,RemoteRegistry,upnphost,SSDPSRV,mspool"
To: LocalService = ""{random values}""
- From: LocalService = "Alerter,WebClient,LmHosts,RemoteRegistry,upnphost,SSDPSRV,mspool"
Step 6
Search and delete this file
- %User Profile%\Application Data\mspool.DLL
Step 7
Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_DROPPER.ZAS. 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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