Backdoor.Penrox

SUMMARY

Backdoor.Penrox is a Backdoor Trojan that allows unauthorized access to a compromised computer.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) August 22, 2001
• Virus Definitions (Intelligent Updater) August 21, 2001

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
• Compromises Security Settings: Allows for unauthorized access to the compromised system.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Backdoor.Penrox is run, it first queries the operating system to determine what its file name is. (See the Additional Information section for details as to why this is necessary.)

This file name is then used by the Trojan when it makes the following change to the Windows registry:

It adds the value

TaskReg  <path and file name of Backdoor.Penrox>

to the key

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun

so that it runs every time that Windows starts.

Next, Backdoor.Penrox sends the hacker information about the infected computer by connecting to an IRC channel that is monitored by the hacker. Also, the compromised system, from that moment on, is listening for commands from the hacker.

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 all files that are detected as Backdoor.Penrox and remove the registry entry that it added.

To remove the Trojan:

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. Be sure that NAV is configured to scan all files.
3. Delete all files that are detected as Backdoor.Penrox.

To edit the registry:

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

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_MACHINESoftwareMicrosoft
   WindowsCurrentVersionRun
   
4. In the right pane, delete the following value:
   
   TaskReg  <path and file name of Backdoor.Penrox>
   
5. Exit the Registry Editor.