BKDR_CHOSZ.C
Windows 2000, Windows XP, Windows Server 2003
Threat Type: Backdoor
Destructiveness: No
Encrypted: Yes
In the wild: Yes
OVERVIEW
Downloaded from the Internet, Dropped by other malware
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.
It executes commands from a remote malicious user, effectively compromising the affected system.
It logs a user's keystrokes to steal information.
It deletes the initially executed copy of itself.
TECHNICAL DETAILS
295,424 bytes
EXE, DLL
Yes
11 Sep 2012
Compromises system security, Connects to URLs/IPs, Steals information
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 and executes them:
- %System Root%\Documents and Settings\All Users\Application Data\Connection.DLL
(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)
Autostart Technique
This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection
Description = "network connect"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection
DisplayName = "Connection"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection
ErrorControl = "1"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection
ImagePath = "%SystemRoot%\system32\svchost.exe -k LocalService"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection
ObjectName = "LocalSystem"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection
Start = "2"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection
Type = "10"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection\Parameters
ServiceDll = "%System Root%\Documents and Settings\All Users\Application Data\Connection.DLL"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection\Parameters
ServiceMain = "VlCo"
Other System Modifications
This backdoor adds the following registry keys:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection\Enum
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection\Parameters
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Connection\Security
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
SS
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
SS\PROXY
It modifies the following registry entries:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
LocalService = "{Default values} Connection"
(Note: The default value data of the said registry entry is {Default values}.)
Backdoor Routine
This backdoor executes the following commands from a remote malicious user:
- Connect to a database server and execute a SQL statement
- Display a message box
- Download files
- Enumerate TCP connections
- Enumerate network shared folders and devices
- Enumerate/create/delete/modify files and folders
- Enumerate/create/delete/modify registry keys and entries
- Enumerate/create/delete/modify/start services
- Enumerate/create/terminate processes
- Get drive information
- Get file information
- Get process information
- Get service information
- Get system information
- Lock windows
- Log keystrokes and active window
- Log off user
- Manage application windows
- Perform remote desktop
- Perform remote shell
- Restart/shutdown system
- Take screenshots of the system
It connects to the following URL(s) to send and receive commands from a remote malicious user:
- {BLOCKED}m.{BLOCKED}e.com
Information Theft
This backdoor logs a user's keystrokes to steal information.
Stolen Information
The stolen information is saved in the following file:
- %System Root%\Documents and Settings\All Users\Application Data\SSK.LOG
(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)
Other Details
This backdoor deletes the initially executed copy of itself
SOLUTION
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
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
- Connection
- Connection
- In HKEY_LOCAL_MACHINE\SOFTWARE\Classes
- SS
- SS
Step 4
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\SvcHost
- From: LocalService = "{Default values} Connection"
To: LocalService = {Default values}
- From: LocalService = "{Default values} Connection"
Step 5
Search and delete this file
- %System Root%\Documents and Settings\All Users\Application Data\SSK.LOG
Step 6
Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_CHOSZ.C. 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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