BKDR_ZEGOST.UASILE
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.
It deletes itself after execution.
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:
- %Windows%\help\dao17.cnt
(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)
Autostart Technique
This Backdoor 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\DCOMEventLauncher\Parameters
Other System Modifications
This Backdoor deletes the following files:
- %Windows%\help\dao17.cnt
(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)
It adds the following registry keys:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\
Services\DCOMEventLauncher\Parameters
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\
Services\DCOMEventLauncher\Parameters
It adds the following registry entries:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
DCOMEventLauncher = "DCOMEventLauncher"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\DCOMEventLauncher\Parameters
ServiceDll = "%Program Files%\COMMON~1\MICROS~1\TextConv\DCOMEV~1.DLL"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\DCOMEventLauncher
Start = "2"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\DCOMEventLauncher
Description = "{random characters}"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\
Services\DCOMEventLauncher\Parameters
ServiceDll = "%Program Files%\COMMON~1\MICROS~1\TextConv\DCOMEV~1.DLL"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\
Services\DCOMEventLauncher
Start = "2"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\
Services\DCOMEventLauncher
Description = "{random characters}"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\
Services\DCOMEventLauncher\Parameters
ServiceDll = "%Program Files%\COMMON~1\MICROS~1\TextConv\DCOMEV~1.DLL"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\
Services\DCOMEventLauncher
Start = "2"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\
Services\DCOMEventLauncher
Description = "{random characters}"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\DCOMEventLauncher
StTime = "2017-10-17 01:05"
Dropping Routine
This Backdoor drops the following files:
- %User Temp%\680703680703.tmp
- %User Temp%\680734680734.tmp
- %User Temp%\680812680812.tmp
(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.)
Other Details
This Backdoor connects to the following possibly malicious URL:
- {BLOCKED}.91.146
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\DCOMEventLauncher
- Parameters
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\DCOMEventLauncher
- Parameters
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\Services\DCOMEventLauncher
- 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\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SvcHost
- DCOMEventLauncher = "DCOMEventLauncher"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\DCOMEventLauncher\Parameters
- ServiceDll = "%Program Files%\COMMON~1\MICROS~1\TextConv\DCOMEV~1.DLL"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\DCOMEventLauncher
- Start = "2"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\DCOMEventLauncher
- Description = "{random characters}"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\DCOMEventLauncher\Parameters
- ServiceDll = "%Program Files%\COMMON~1\MICROS~1\TextConv\DCOMEV~1.DLL"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\DCOMEventLauncher
- Start = "2"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\DCOMEventLauncher
- Description = "{random characters}"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\Services\DCOMEventLauncher\Parameters
- ServiceDll = "%Program Files%\COMMON~1\MICROS~1\TextConv\DCOMEV~1.DLL"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\Services\DCOMEventLauncher
- Start = "2"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\Services\DCOMEventLauncher
- Description = "{random characters}"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\DCOMEventLauncher
- StTime = "2017-10-17 01:05"
Step 5
Search and delete these components
- %User Temp%\680703680703.tmp
- %User Temp%\680734680734.tmp
- %User Temp%\680812680812.tmp
Step 6
Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_ZEGOST.UASILE. 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 7
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.
- %Windows%\help\dao17.cnt
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