Backdoor.IRC.Critical

SUMMARY

Backdoor.ICR.Critical is a backdoor Trojan horse that allows unauthorized access to a compromized system. It allows a hacker to control your computer using Internet Relay Chat (IRC).

Protection

• Virus Definitions (LiveUpdate™ Weekly) September 18, 2001
• Virus Definitions (Intelligent Updater) September 18, 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
• Modifies Files: The Win.ini is used as a loading point.
• Compromises Security Settings: Allows unauthorized access to a compromised system.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Normally, this backdoor Trojan horse is distributed as one large installation executable. Once run, this executable pretends to install a benign antivirus program, while in the background it installs the backdoor files in various places on the system.

The inserted files are:

• C:WindowsDskLoad.exe
• C:WindowsPrun.exe
• C:WindowsSys.exe
• C:Program FilesAccessoriesBackupSystemCriticalCons1.dll
• C:Program FilesAccessoriesBackupSystemCriticalDeg326.dll
• C:Program FilesAccessoriesBackupSystemCriticalExpl32.exe
• C:Program FilesAccessoriesBackupSystemCriticalExplorer2.exe
• C:Program FilesAccessoriesBackupSystemCriticalins.dll
• C:Program FilesAccessoriesBackupSystemCriticalMir436.dll
• C:Program FilesAccessoriesBackupSystemCriticalMirc.ini
• C:Program FilesAccessoriesBackupSystemCriticalMoo.dll
• C:Program FilesAccessoriesBackupSystemCriticalMstg1.dll
• C:Program FilesAccessoriesBackupSystemCriticalScan31.dll
• C:Program FilesAccessoriesBackupSystemCriticalUpdatex1.dll
• C:Program FilesAccessoriesBackupSystemCriticalWin32x.dll
• C:Program FilesAccessoriesBackupSystemCriticalWinexp32.dll
• C:Program FilesAccessoriesBackupSystemCriticalWinvar32.dll

NOTE: Most of the .dll files in this list are not dynamic link libraries but are IRC script files and other data files.

All the files in the C:Program FilesAccessoriesBackupSystemCritical folder are created with "Hidden" attributes, in an attempt to escape being noticed. In order to gain control of the compromised system, this Trojan horse does the following:

• It modifies the run= line of the C:WindowsWin.ini file so that it becomes:
  
  run=C:WindowsDskLoad.exe
  
• It makes the following modifications to the registry:
  
  • In the key
    
    HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionUninstallmIRC
    
    it adds or modifies the value
    
    DisplayName mIRC
    
  • In the key
    
    HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionUninstallmIRC
    
    it adds or modifies the value
    
    UninstallString c:program filesaccessoriesackupsystemcriticalexpl32.exe" -uninstall"
    
  • In the key
    
    HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
    
    it adds the value
    
    StubPath C:WindowsDskLoad.exe
    
  • In the key
    
    HKEY_LOCAL_MACHINESoftwareMicrosoftActive SetupInstalled ComponentsKeyName
    
    it adds or modifies the value
    
    MSSysDisk C:WindowsDskLoad.exe
    
  • Finally, IRC file extensions are hooked in HKEY_LOCAL_MACHINESoftwareClasses that call "c:program filesaccessoriesackupsystemcriticalexpl32.exe" when chat files are opened.

The inserted file C:WindowsSys.exe is waiting for the user or a program to call the "sys" command. In DOS-based operating systems, the file Sys.com is used to make a data medium DOS bootable. On Windows computers, this file would reside in C:WindowsCommandsys.com. However, when running "sys" from the command prompt, the viral C:WindowsSys.exe is run instead of the proper C:WindowsCommandsys.com.

This viral sys.exe installs Backdoor.Subseven.22 on the system allowing for even more control over the compromised system.

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

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
3. Run a full system scan.
4. Delete all files that are detected as
5. Backdoor.IRC.Critical or Backdoor.Subseven.22. Deleted files will have to be replaced from a clean backup or reinstalled.
6. Remove the changes that it made to the registry changes and the modifications to the Win.ini file.