Win32/Lethic is a trojan that connects to remote servers, which may lead to unauthorized access to an affected system.
System changes
The following system changes may indicate the presence of this malware:
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The presence of the following files:
<system folder>\shelldm.exe
<system folder>\xcllsx.exe
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The presence of the registry modifications such as the following examples:
In subkey: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Sets value: "Taskman"
With data: "<malware path and file name>"
In subkey: HKCU\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Sets value: "Shell"
With data: "explorer.exe,<malware path and file name>"
In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Sets value: "<value>"
With data: "<malware path and file name>"
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Open connections with unfamiliar hosts via TCP ports 1430, 8090 or other
Win32/Lethic is a trojan that connects to remote servers, which may lead to unauthorized access to an affected system.
Installation
Variants of Win32/Lethic may drop copies of itself with different file names in the Windows system folder, for example:
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<system folder>\shelldm.exe
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<system folder>\xcllsx.exe
Note: <system folder> refers to a variable location that is determined by the malware by querying the Operating System. The default installation location for the System folder for Windows 2000 and NT is C:\Winnt\System32; and for XP and Vista is C:\Windows\System32.
It creates entries in the system registry to ensure that its dropped copies run every time Windows starts:
In subkey: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Sets value: "Taskman"
With data: "<malware path and file name>"
In subkey: HKCU\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Sets value: "Shell"
With data: "explorer.exe,<malware path and file name>"
In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Sets value: "<value>"
With data: "<malware path and file name>"
For example:
In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Sets value: "zmmclr"
With data: "<system folder>\xcllsx.exe"
In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Sets value: "wesspell"
With data: "<system folder>\shelldm.exe"
In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Sets value: "qscmdll"
With data: "<system folder>\ssmcdsw.exe"
It injects its code into the 'explorer.exe' process.
Payload
Connects to a remote server
Win32/Lethic attempts to establish a connection to remote servers through various TCP ports. For example:
- Attempts connecting to 'lycomputing.com' via TCP port 1430
- Attempts connecting to 'nuygtfcwq.com' via TCP port 8900
- Attempts connecting to 'dqglobex.com' via TCP port 8090
Some of the remote sites it attempts to connect to are:
b1ijh7hifd.com
btceswqdw.com
bydvwqcdw.com
lxforbug.com
dqglobex.com
iamnothere.cn
lycomputing.com
miniknfdw.com
mojujfdhew.com
nhi8ho9lbnw.com
nuygtfcwq.com
sometimesgood.com
uckybusy.com
verywellhere.cn
Once connected, it may allow remote access and control of an affected computer.
Analysis by Scott Molenkamp
Take the following steps to help prevent infection on your computer:
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Enable a firewall on your computer.
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Get the latest computer updates for all your installed software.
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Use up-to-date antivirus software.
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Limit user privileges on the computer.
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Use caution when opening attachments and accepting file transfers.
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Use caution when clicking on links to webpages.
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Avoid downloading pirated software.
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Protect yourself against social engineering attacks.
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Use strong passwords.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.
You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
Use up-to-date antivirus software
Limit user privileges on the computer
Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.
You can configure UAC in your computer to meet your preferences:
Use caution when opening attachments and accepting file transfers
Exercise caution with email and attachments received from unknown sources, or received unexpectedly from known sources. Use extreme caution when accepting file transfers from known or unknown sources.
Use caution when clicking on links to webpages
Exercise caution with links to webpages that you receive from unknown sources, especially if the links are to a webpage that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a webpage with harmful content.
Avoid downloading pirated software
Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see '
The risks of obtaining and using pirated software'.
Protect yourself from social engineering attacks
While attackers may attempt to exploit vulnerabilities in hardware or software to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted computer. For more information, see '
What is social engineering?'.
Use strong passwords
Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least eight characters, and combines letters, numbers, and symbols. For more information, see
http://www.microsoft.com/protect/yourself/password/create.mspx.
To detect and remove this threat and other malicious software that may be installed on your computer, run a full-system scan with an appropriate, up-to-date, security solution. The following Microsoft products will detect and remove this threat:
