RingZero.Trojan

SUMMARY

This Trojan runs as a hidden process, and it sends and retrieves data over an Internet connection.

Protection

• Virus Definitions (Intelligent Updater) October 26, 1999

Threat Assessment

Wild

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

Damage

• Damage Level: Low

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

There are three versions of the Trojan horse:

• Its.exe
  Its.exe copies itself to the WindowsSystem folder when executed for the first time. It also drops the Ring0.vxd file into the same folder. Its.exe is executed again the next time that Windows starts. At this time, it creates another file to hold its data, Its.dat. It then tries to connect to two Web sites that contain strings that attempt to send mail to an address at a pager service using the Microsoft mail server.
  
• Pst.exe
  Pst.exe installs itself in the same manner as Its.exe, and also drops the Ring0.vxd file into the same folder. It attempts to connect to a different Web site than those that Its.exe tries to access.
  
• Telnet23.exe
  Telnet23.exe is another version that appears to steal Windows cached passwords. It attempts to reach a Web site and send email.

These Trojans can be packed within other host programs. When you run the host program, the Trojan is installed on the computer. RingZero hides its process by registering itself as a Windows service, so it is not displayed in the Windows task manager. It also hides its entry in the Windows registry. If the Trojan is not running, the startup call in the registry Run key is visible.

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 this Trojan, delete files detected as RingZero.Trojan, and remove references from the Run key.

To delete the files:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and run a full system scan, making sure that NAV is set to scan all files.
3. Delete any files detected as RingZero.Trojan. If NAV is not able to delete the files, do the following:
   1. Write down the names and locations of the files that NAV detected.
   2. Restart the computer in MS-DOS mode, or boot to a clean DOS boot floppy disk.
   3. Delete the detected files from the WindowsSystem folder.
   4. Delete the Its.dat and Ring0.dat files from the WindowsSystem folder.
   5. Restart Windows.

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 click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the following key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, look for the following values, and if found, delete them:
   
   DK32 support PST "pst.exe"
   DK32 support ITS "its.exe"
   Description of EPS II "telnet23.exe"