WORM_LECNA.A
Worm:Win32/Levsha.A (Microsoft), W32.Lecna.H (Symantec)
Windows 2000, Windows XP, Windows Server 2003

Threat Type: Worm
Destructiveness: No
Encrypted: Yes
In the wild: Yes
OVERVIEW
Propagates via removable drives
This worm arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
It modifies certain registry entries to hide file extensions.
It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.
It executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system. As of this writing, the said sites are inaccessible.
TECHNICAL DETAILS
Varies
PE
Yes
22 Sep 2008
Drops files, Downloads files, Terminates processes, Modifies system registry
Arrival Details
This worm 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 worm drops the following copies of itself into the affected system:
- %System%\Recycler.exe
(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)
It drops the following component file(s):
- %System%\uninstx.exe - also detected as WORM_LECNA.A
- %System%\confi.exe - also detected as WORM_LECNA.A
- %System%\{random file name}.dll - also detected as WORM_LECNA.A
(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)
It drops the following non-malicious files:
- %System%\Config.ini
- %System%\AUTORUN.INF - used as the master copy of the AUTORUN.INF dropped in removable drives
(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)
Its DLL component is injected to the following process(es):
- explorer.exe
Autostart Technique
This worm adds the following registry entries to enable its automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Recycled = "%System%\Recycler.exe"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
uninstx.exe = "%System%\uninstx.exe"
Other System Modifications
This worm adds the following registry keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
NetWorkSetup
It adds the following registry entries:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
NetWorkSetup
pid = "{random string}"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
NetWorkSetup
hostid = {random number}
It modifies the following registry entries to hide file extensions:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
HideFileExt = "1"
(Note: The default value data of the said registry entry is 0.)
Propagation
This worm drops the following copy(ies) of itself in all removable drives:
- {removable drive letter}:\Recycler.exe
It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.
The said .INF file contains the following strings:
[autorun]
open=Recycler.exe
shellexecute=Recycler.exe
shell\Auto\command=Recycler.exe
shell=Auto
Process Termination
This worm terminates the following processes if found running in the affected system's memory:
- amon.exe
- armor2net.exe
- avgfwsrv.exe
- avp.exe
- blackd.exe
- blackice.exe
- bullguard.exe
- capfaem.exe
- ccapp.exe
- firesvc.exe
- fsaw.exe
- guard.exe
- kavpf.exe
- kavpfw.exe
- lpfw.exe
- mcagent.exe
- mpeng.exe
- npfsvice.exe
- ofcpfwsvc.exe
- outpost.exe
- pccguide.exe
- persfw.exe
- pf4.exe
- pnmsrv.exe
- rfwsrv.exe
- smc.exe
- sspfwtry2.exe
- swagent.exe
- tmpfw.exe
- winaw32.exe
- winroute.exe
- zlclient.exe
Download Routine
This worm accesses the following websites to download files:
- http://www.{BLOCKED}c.com/thrMilitary/thrapp.htm
- http://www.{BLOCKED}c.com/thrMilitary/thrmyapp.htm
It saves the files it downloads using the following names:
- %Windows%\netscv.exe
- %Windows%\netsvcs.exe
(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)
It then executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.
As of this writing, the said sites are inaccessible.
NOTES:
It connects to following URLs to remotely inform a malicious user of its installation:
- http://{BLOCKED}h.com.cn/thrMilitary/thrconnect.gif
- http://www.{BLOCKED}c.com/thrMilitary/thrhostlist.htm
- devvect.dll
- funcdev.dll
- gatwaysh.dll
- getkbsyn.dll
- getspi.dll
- hostip2.dll
- kbpool.dll
- kbtype.dll
- keylsv.dll
- keyvect.dll
- lancheck.dll
- mcdirect8.dll
- mcfetch.dll
- missnetp.dll
- mousegrl.dll
- mpeg2fun.dll
- msrctr.dll
- netunnel.dll
- routersh.dll
- tcpproto.dll
- udpsh.dll
- vpntunnel.dll
SOLUTION
8.900
5.558.04
22 Sep 2008
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
Restart in Safe Mode
Step 3
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 Recycled="%System%\Recycler.exe"
- Windows Recycled="%System%\Recycler.exe"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
- uninstx.exe="%System%\uninstx.exe"
- uninstx.exe="%System%\uninstx.exe"
Step 4
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\CurrentVersion\Explorer\Advanced
- From: HideFileExt="1"
To: HideFileExt="0"
- From: HideFileExt="1"
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\SOFTWARE\Microsoft
- NetWorkSetup
- NetWorkSetup
Step 6
Search and delete these files
Step 7
Search and delete AUTORUN.INF files created by WORM_LECNA.A that contain these strings
Step 8
Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_LECNA.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.
Did this description help? Tell us how we did.