Backdoor.WLF

SUMMARY

Backdoor.WLF is a backdoor program that works along with Backdoor.NTHack.

Protection

• Virus Definitions (Intelligent Updater) April 16, 2001

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Low
• Degrades Performance: Excessive internet access occurs.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Backdoor.WLF is normally installed remotely by another user. It also utilizes a UPX packed version of the legitimate WinGate application to do its job. Once Backdoor.WLF is installed, it allows other users to access the internet through the victimized computer. The victimized computer may then start acting like a proxy server. A possible malicious application of this feature is for a remote user to perform unauthorized downloads on this victimized computer, making it look legitimate, since it would be requested by an acting proxy server.

Recommendations

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.

REMOVAL

To remove the worm, delete any files detected as Backdoor.WLF, and undo the changes that it made to the registry. Further removal instructions that apply to both this Backdoor as well as Backdoor.NTHack are available in the writeup for Backdoor.NTHack.

To remove the worm:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and then run a full system scan, making sure that NAV is set to scan all files.
3. Delete any files detected as Backdoor.WLF.

To edit the registry:

CAUTION: We strongly recommend that you back up the system registry before making any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure you modify only the keys specified.

Please see the document How to back up the Windows registry before proceeding.

1. Click Start, and then click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the following subkey:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindows NTCurrentVersionWinlogon
   
   
4. In the right pane, delete the following value:
   
   NewGina
   
5. Click Registry and then click Exit to save the changes