BKDR_KULUOZ.KLA
Windows
Threat Type: Backdoor
Destructiveness: No
Encrypted:
In the wild: Yes
OVERVIEW
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.
TECHNICAL DETAILS
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:
- %User Profile%\Application Data\Windows Update.exe
(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 System Modifications
This backdoor deletes the following files:
- %User Temp%\ notepad.exe
- %User Temp%\#folder#\#rundll32 .exe#:Zone.Identifier
- %User Startup%\#rundll32 .exe#:Zone.Identifier
- %User Profile%\Application Data\Windows Update.exe
(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.. %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.)
It adds the following registry keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ESENT\Process\tmp
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ESENT\Process\tmp\
DEBUG
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ESENT\Process\Windows Update
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ESENT\Process\Windows Update\
DEBUG
It modifies the following registry entries:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Eventlog\Application\
ESENT
EventMessageFile = "%System%\ESENT.dll"
(Note: The default value data of the said registry entry is {random values}.)
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Eventlog\Application\
ESENT
CategoryMessageFile = "%System%\ESENT.dll"
(Note: The default value data of the said registry entry is {random values}.)
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Eventlog\Application\
ESENT
CategoryCount = "1"
(Note: The default value data of the said registry entry is 10.)
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Eventlog\Application\
ESENT
TypesSupported = "7"
(Note: The default value data of the said registry entry is 7.)
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = "1"
(Note: The default value data of the said registry entry is 2.)
Dropping Routine
This backdoor drops the following files:
- %User Temp%\tmp.exe
- %User Temp%\SysInfo.txt
- %User Profile%\Application Data\pid.txt
- %User Profile%\Application Data\pidloc.txt
(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %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 backdoor connects to the following possibly malicious URL:
- {BLOCKED}.248.172
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
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\SOFTWARE\Microsoft\ESENT\Process
- tmp
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ESENT\Process\tmp
- DEBUG
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ESENT\Process
- Windows Update
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ESENT\Process\Windows Update
- DEBUG
Step 3
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\SYSTEM\ControlSet001\Services\Eventlog\Application\ESENT
- From: EventMessageFile = "%System%\ESENT.dll"
To: EventMessageFile = ""{random values}""
- From: EventMessageFile = "%System%\ESENT.dll"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Eventlog\Application\ESENT
- From: CategoryMessageFile = "%System%\ESENT.dll"
To: CategoryMessageFile = ""{random values}""
- From: CategoryMessageFile = "%System%\ESENT.dll"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Eventlog\Application\ESENT
- From: CategoryCount = "1"
To: CategoryCount = ""10""
- From: CategoryCount = "1"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Eventlog\Application\ESENT
- From: TypesSupported = "7"
To: TypesSupported = ""7""
- From: TypesSupported = "7"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: Hidden = "1"
To: Hidden = ""2""
- From: Hidden = "1"
Step 4
Search and delete these components
- %User Temp%\tmp.exe
- %User Temp%\SysInfo.txt
- %User Profile%\Application Data\pid.txt
- %User Profile%\Application Data\pidloc.txt
Step 5
Scan your computer with your Trend Micro product to delete files detected as BKDR_KULUOZ.KLA. 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 6
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%\ notepad.exe
- %User Temp%\#folder#\#rundll32 .exe#:Zone.Identifier
- %User Startup%\#rundll32 .exe#:Zone.Identifier
- %User Profile%\Application Data\Windows Update.exe
Did this description help? Tell us how we did.