BKDR_LAYORK.AB
TrojanSpy:Win32/Embed.A (Microsoft);Backdoor.Layork (Symantec); Trojan.Win32.Agent.cxhf (Kaspersky)
Windows 2000, Windows XP, Windows Server 2003
Threat Type: Backdoor
Destructiveness: No
Encrypted: Yes
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 executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.
It connects to certain websites to send and receive information.
TECHNICAL DETAILS
48,128 bytes
EXE
Yes
22 Jun 2011
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 files:
- %Application Data%\Windows Update\logs.ini
- %Application Data%\Windows Update\wininit.dll - detected as TROJ_ORSAM.BIX
(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)
It drops the following copies of itself into the affected system:
- %Application Data%\Windows Update\wininit32.exe
- %Application Data%\sysinfo.dat
(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)
It creates the following folders:
- %Application Data%\Windows Update
- %Application Data%\Windows Update\logs
(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)
It is injected into the following processes running in memory:
- explorer.exe
It terminates the execution of the copy it initially executed and executes the copy it drops instead.
Autostart Technique
This backdoor adds the following registry entries to enable its automatic execution at every system startup:
HKEY_CURRENT_USER\Software\Classes\
Software\Microsoft\Windows NT\
CurrentVersion\Windows
load = %Application Data%\Windows Update\wininit32.exe
It modifies the following registry entries to ensure it automatic execution at every system startup:
HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Windows
load = %Application Data%\Windows Update\wininit32.exe
(Note: The default value data of the said registry entry is {blank}.)
Dropping Routine
This backdoor sets the attributes of its dropped file(s) to the following:
- Hidden
- System
- Read Only
It executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.
Other Details
This backdoor connects to the following website to send and receive information:
- http://{BLOCKED}bar.dns0755.net/{BLOCKED}supdatev7/search{random}
SOLUTION
8.900
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
Remove malware files dropped/downloaded by BKDR_LAYORK.AB
Step 3
Scan your computer with your Trend Micro product and note files detected as BKDR_LAYORK.AB
Step 4
Restart in Safe Mode
Step 5
Search and delete these folders
- %Application Data%\Windows Update
Step 6
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_CURRENT_USER\Software\Classes\Software\Microsoft\Windows NT\CurrentVersion\Windows
- load = %Application Data%\Windows Update\wininit32.exe
- load = %Application Data%\Windows Update\wininit32.exe
Step 7
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_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows
- From: load = %Application Data%\Windows Update\wininit32.exe
To: load ={blank}
- From: load = %Application Data%\Windows Update\wininit32.exe
Step 8
Search and delete this file
Step 9
Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_LAYORK.AB . 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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