Backdoor.Upfudoor

SUMMARY

Backdoor.Upfudoor is a Backdoor Trojan that gives an attacker unauthorized access to a compromised computer. By default, it opens port 39,122. The Trojan has the ability to log keystrokes. It is packed with ASPack v2.11.

Protection

• Virus Definitions (LiveUpdate™ Weekly) December 24, 2002
• Virus Definitions (Intelligent Updater) December 23, 2002

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: Medium
• Modifies Files: Modifies system registry.
• Releases Confidential Info: Intercept confidential information by hooking any keystrokes.
• Compromises Security Settings: Allows unauthorized access to the compromised machine.

Distribution

• Distribution Level: Low
• Ports: 39122

TECHNICAL DETAILS

When Backdoor.Upfudoor runs, it performs the following actions:

1. Copies itself as %system%Kernel32.exe.
   
   NOTE: %system% is a variable. The Trojan locates the System folder and copies itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
   
2. The Trojan creates the value
   
   kernel32.dll    %system%kernel32.exe
   
   in the registry key
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the Trojan starts when you start or restart Windows.
   
3. If the operating system is Windows 95/98/Me: Registers itself as a service process to continue running after you log off. In this case, Backdoor.Upfudoor will only close when the system is shut down.
4. Attempts to obtain an access to the password cache stored on the local computer. The cached passwords include modem and dialup passwords, URL passwords, share passwords, and others.
5. Inventories successfully established RAS connection details to authenticate its access to the remote access server.
6. Installs hook procedures into a hook chain to monitor the system for any keyboard and mouse messages. This permits Backdoor.Upfudoor to intercept any key strokes.

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

These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Do one of the following:
   • Windows 95/98/Me: Restart the computer in Safe mode.
   • Windows NT/2000/XP: End the Trojan process.
3. Run a full system scan and delete all the files detected as Backdoor.Upfudoor.
4. Reverse the change that the Trojan made to the registry.
   

For further details, read the following instructions.

Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain the virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate) line at the top of this writeup.
• Downloading the definitions using the Intelligent Updater. The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater) line at the top of this writeup.
  
  The Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

Restarting the computer in Safe mode or ending the Trojan process

Windows 95/98/Me
Restart the computer in Safe mode. All Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions, read the document, How to start the computer in Safe Mode.

Windows NT/2000/XP
To end the Trojan process:
1. Press Ctrl+Alt+Delete once.
2. Click Task Manager.
3. Click the Processes tab.
4. Double-click the Image Name column header to alphabetically sort the processes.
5. Scroll through the list and look for kernel32.dll.
6. If you find the file, click it, and then click End Process.
7. Exit the Task Manager.
   

Scanning for and deleting the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
2. For Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • For Symantec AntiVirus Enterprise products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
3. Run a full system scan.
4. If any files are detected as infected with Backdoor.Upfudoor, click Delete.

Reversing the changes made to the registry

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, How to make a backup of the Windows registry, for instructions.

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 key
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the value
   
   kernel32.dll    %system%kernel32.exe
   
5. Exit the Registry Editor.