BKDR_ZEGOST.TIDAFAT
Backdoor:Win32/Zegost (Microsoft)
Windows
Threat Type: Backdoor
Destructiveness: No
Encrypted: No
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 may be dropped by other malware.
As of this writing, the said sites are inaccessible.
It deletes the initially executed copy of itself.
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.
It may be dropped by the following malware:
- TROJ_DLOADR.AUSUML
Installation
This Backdoor drops the following files:
- %User Temp%\{random numbers}.vbs - deletes malware copy
(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.)
It drops the following copies of itself into the affected system:
- %Program Files%\DFnsa.exe
(Note: %Program Files% is the Program Files folder, where it usually is C:\Program Files on all Windows operating system versions; C:\Program Files (x86) for 32-bit applications running on Windows 64-bit operating systems.)
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\{random name}
Description = {random}
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random name}
MarkTime = {yyyy-mm-dd hh:mm}
It adds and runs the following services:
- Service path: %Program Files%\DFnsa.exe
- Service name: {random}
(Note: %Program Files% is the Program Files folder, where it usually is C:\Program Files on all Windows operating system versions; C:\Program Files (x86) for 32-bit applications running on Windows 64-bit operating systems.)
It 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\{random name}
Download Routine
This Backdoor connects to the following URL(s) to download its component file(s):
- http://ca.{BLOCKED}sh.org:443/NetSyst96.dll
It saves the files it downloads using the following names:
- %Program Files%\AppPatch\mysqld.dll (or {drive letter}\Program Files\AppPatch\mysqld.dll)
(Note: %Program Files% is the Program Files folder, where it usually is C:\Program Files on all Windows operating system versions; C:\Program Files (x86) for 32-bit applications running on Windows 64-bit operating systems.)
As of this writing, the said sites are inaccessible.
Other Details
This Backdoor deletes the initially executed copy of itself
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
Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.
Step 3
Remove the malware/grayware file that dropped/downloaded BKDR_ZEGOST.TIDAFAT. (Note: Please skip this step if the threat(s) listed below have already been removed.)
- TROJ_DLOADR.AUSUML
Step 4
Restart in Safe Mode
Step 5
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
- {random name}
- {random name}
Step 6
Search and delete this file
- %Program Files%\AppPatch\mysqld.dll
- {drive letter}\Program Files\AppPatch\mysqld.dll
- %User Temp%\{random numbers}.vbs
Step 7
Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_ZEGOST.TIDAFAT. 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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