BKDR_LAYRUI.A
Backdoor: Win32/Layrui.A (Microsoft), Win32/Autoit.NFV trojan (ESET)
Windows
Threat Type: Backdoor
Destructiveness: No
Encrypted: No
In the wild: Yes
OVERVIEW
This backdoor deletes autostart registry entries associated with the processes it terminates to completely disable applications.
It may also connect to Internet Relay Chat (IRC) servers and receive commands from a remote user.
It deletes the file(s) associated with the process(es) it terminates. It does the said routine to completely disable programs and applications.
TECHNICAL DETAILS
778287 bytes
, EXE
Yes
03 Apr 2013
Compromises system security, Connects to URLs/IPs, Downloads files
Installation
This backdoor drops the following copies of itself into the affected system:
- %Windows%\system32\svihost.exe
(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)
Autostart Technique
This backdoor adds the following registry entries to enable its automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Updates = "%Windows%\system32\svihost.exe"
Other System Modifications
This backdoor deletes the following files:
- %Windows%\system32\update.exe
- %Windows%\system32\server.txt
- %Windows%\server.txt
- %Windows%\system32\check.txt
(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)
It adds the following registry entries as part of its installation routine:
HKEY_CURRENT_USER\Software\Policies\
Microsoft\Internet Explorer\Control Panel
Homepage = 0
HKEY_LOCAL_MACHINE\Software\Policies\
Microsoft\Internet Explorer\Control Panel
Homepage = 0
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = 0
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = 0
HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = 0
HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = 0
HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Internet Explorer\Main
Start Page = "http://autokiemthe.com"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Start Page = "http://autokiemthe.com"
It deletes autostart registry entries associated with the processes it terminates to completely disable applications.
It deletes the following registry keys:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Updates =
HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Update =
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Update =
HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Updates =
HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Internet Explorer\Main
Window Title =
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Window Title =
Backdoor Routine
This backdoor may also connect to Internet Relay Chat (IRC) servers and receive commands from a remote user.
It accesses a remote Internet Relay Chat (IRC) server where it receives the following commands from a remote malicious user:
- Quit – wait for another backdoor command
- Exit – closes the TCP connection
- logout – asks the remote malicious user to logout. This will disable all backdoor commands.
- run – executes a file that is not visible to the user
- check – checks if specified process is running
- master – display connected user and channel
- login - asks the remote malicious user to login. Correct password enables all backdoor commands. cmd - open a remote shell
- Download - downloads a file
- Update - same function as Download
- rundos - execute dos command
- abort - stops current download
- pl - lists all running processes
- openhost - setups ftp
- chupinh - Screen capture then send file to remote malicious user via ftp
- Getfile - uploads file in ftp
- cp - close process
- ddos - download and execute file "%Windows%\system32\ddosw.exe"
- stop - uninstall "%Windows%\system32\ddosw.exe" from the system
- Visit - access a website using Internet Explorer
- shutdown - shuts down the system
- reboot - reboots the system
- Del - delete a file
- Copy - copy a file
- Move - move a file
- info - lists system information of the user (e.g. OS Version, Computer Name, UserName, IP Address) Chat - enables chat
- Ver - displays the malware version
- Help - lists all backdoor commands
(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)
Process Termination
This backdoor terminates the following processes if found running in the affected system's memory:
- FastHelper.exe
- bdss.exe
- svchosts.exe
- svhost.exe
- svhcost.exe
- svchos.exe
- at4kt.exe
- Hackchucphuc.exe
- Bkav2006.exe
- Wupdate.exe
- EtherD.exe
It terminates the following malware-related processes:
- svihost.exe
- Dangkysudung.exe
It deletes the file(s) associated with the process(es) it terminates. It does the said routine to completely disable programs and applications.
Download Routine
This backdoor downloads an updated copy of itself from the following website(s):
- http://{BLOCKED}viet.com/alo/svihost.exe
- http://{BLOCKED}ip.com/alo/update.exe
It connects to the following URL(s) to download its configuration file:
- http://{BLOCKED}viet.com/bot1/dunghoitaisao.php
- http://{BLOCKED}ip.com/alo/dunghoitaisao.php
It saves the files it downloads using the following names:
- %Windows%\system32\check.txt
- %Windows%\system32\update.exe
(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)
Other Details
This backdoor closes application windows that contain the following strings in the title bar:
- EtherDetect Packet Sniffer
It sets the attributes of the following file(s) to Hidden and System:
- %Windows%\system32\svihost.exe
(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)
NOTES:
This backdoor removes the following processes from being displayed in Windows Task Manager:
- svihost.exe
- Dangkysudung.exe
SOLUTION
9.700
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
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 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\CurrentVersion\Run
- Windows Updates = "%Windows%\system32\svihost.exe"
- Windows Updates = "%Windows%\system32\svihost.exe"
- In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet Explorer\Main
- Start Page = "http://autokiemthe.com"
- Start Page = "http://autokiemthe.com"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
- Start Page = "http://autokiemthe.com"
- Start Page = "http://autokiemthe.com"
Step 5
Search and delete this file
- %Windows%\system32\svihost.exe
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.
- %Windows%\system32\svchosts.exe
- %Windows%\system32\svhost.exe
- %Windows%\system32\svhcost.exe
- %Windows%\system32\svchos.exe
- %Windows%\at4kt.exe
- %Windows%\system32\at4kt.exe
- %Windows%\system32\Hackchucphuc.exe
- %Program Files%\Bkav2006\Bkav2006.exe
- %Windows%\system32\Wupdate.exe
- %Windows%\Wupdate.exe
Step 7
Scan your computer with your Trend Micro product to delete files detected as BKDR_LAYRUI.A. 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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