W32.ElKern.4926

W32.ElKern.4926 is associated with W32.Klez.H@mm worm. The worm creates a pure viral body of the virus, using a random file name, in the C:\Program Files folder and activates it. Then the virus runs on its own.

Like W32.ElKern.3326 and W32.ElKern.3587, W32.ElKern.4926 is also a cavity infector that infects randomly chosen Portable Executable (PE) files in folders and subfolders. It begins searching for files to infect in the current folder. It then searches through drive letters, beginning with a random letter and continuing until Z is reached. It can also infect files in open shares on the local network. Some infected files do not change in size.

The file search skips folders whose names contain "rary Inter" or "tem32\dllcac". Additionally, files are skipped if they begin with any of the following: _avp, aler, amon, anti, nod3, npss, nres, nsch, n32s, avwi, scan, f-st, f-pr, avp, or nav.

W32.ElKern.4926 considers a file to be infectable if it is a PE GUI or console application that is not a .dll, does not contain the text "irus", is not protected by the System File Checker that is present in Windows 98/Me/2000/XP, and is neither a WinZip nor a RAR self-extractor.

W32.ElKern.4926 contains a bug that causes files to be infected repeatedly. This can result in infected files that cannot be repaired.

Also, this variant of the virus attempts to insert its code into all running processes. This can result in files being reinfected after a full system scan has found no viruses.

Unlike variants W32.ElKern.3326 and W32.ElKern.3587 which drop Wqk.dll or Wqk.exe and add a value that refers to them in the registry key

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrrentVersion\Run

W32.ElKern.4926 does not drop Wqk.dll or Wqk.exe, and it does not modify any registry keys.

W32.ElKern.dam is a detection for a W32.ElKern.4926 infection in which the file has either been corrupted by the virus W32.Elkern.4926, or the virus body is contained within the file, but the viral code never gains control from the host program.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
• 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.
• Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
• Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
• Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
• Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
• If a 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate compromised computers quickly to prevent threats from spreading further. 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 Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
• For further information on the terms used in this document, please refer to the Security Response glossary.

Summary