W2K.Infis.4608 | 
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The WNT.Infis.4608 virus was updated to support the OEM version of Windows 2000 build 2195, and also fixes a few small bugs in the original release. This update, W2K.Infis.4608, is the first known virus to run in Kernel-mode under Windows 2000 (its predecessor was the first known Windows NT Kernel-mode virus).
Distribution
W2K.Infis is a memory resident parasitic Windows 2000 Kernel-mode driver virus. It operates under Windows 2000 only and will likely fail under the first service pack. The virus does not have any payload.
The virus executes while the user is logged on with Administrator privileges (or equivalent) so that it can install its kernel mode component. Without these priveleges, the virus is unable to install itself or infect other files because it does not contain a User mode replication component.
The virus creates a registry entry named HKLM\System\CurrentControlSet\Services\inf, and also creates a file named inf.sys in this directory: \Winnt\System32\Drivers.
The inf.sys file is a native Windows 2000 Kernel-mode driver, and its size is 4608 bytes. Once the system is restarted, the virus driver (inf.sys) is loaded into memory automatically.
The virus hooks a Kernel mode file open API using a nonstandard method and infects the 32-bit Portable Executable applications with an .exe file name that are accessed "on the fly". The virus will not infect cmd.exe, and is also unable to infect a file that has a read-only attribute. The virus fails to infect some applications properly, and as a result some of the application fails to execute properly. This makes the virus easily noticeable on a system.
The virus driver can be disabled manually by going to the Computer Management\Device Manager entry. The View options need to be changed to Show hidden devices and Device by connection type should be selected in order to see the inf driver name:
Once the driver is disabled, the infected files should be detected and replaced from clean backups.
Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":
- Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
- If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
- Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
- Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
- Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
- Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
- Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
If you believe you have been infected, please download the latest virus definitions via LiveUpdate or from the Symantec Security Response Web site.
- Click here for instructions on using LiveUpdate to retrieve virus definitions.
- Click here to manually download and install virus definitions from the Symantec Security Response Web site.
Write-up by: Peter Szor
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