Backdoor.IRC.Zcrew

SUMMARY

Backdoor.IRC.Zcrew is a backdoor Trojan Horse that is similar to other backdoor IRC Trojans, such as Backdoor.IRC.Aladinz and Backdoor.IRC.Flood.

Backdoor.IRC.Zcrew is written as an IRC script and uses the mIRC client to connect to the Internet, where it notifies the attacker of its presence. The hacker can send various commands to an infected computer and take full control over it.

An infected computer can also be used to launch a ping flood attack against another computer at a specified IP address.

Protection

• Virus Definitions (LiveUpdate™ Weekly) February 19, 2003
• Virus Definitions (Intelligent Updater) February 14, 2003

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
• Compromises Security Settings: Allows unauthorized access to an infected computer.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Backdoor.IRC.Zcrew is executed, it performs the following actions:

1. Loads the script of Backdoor.IRC.Zcrew through mIRC.
   
   
2. Creates the following files:
   
   
   • %System%Bootdrv.dll *
   • %System%Explore.dat
   • %System%Explore.exe
   • %System%Explorer.exe *
   • %System%Iiscache.dll
   • %System%Libparse.exe*
   • %System%Moo.dll *
   • %System%Navdb.dbx
   • %System%Psexec.exe *
   • %System%Rcfg.ini
   • %System%Rconnect.conf
   • %System%Rconnect.exe
   • %System%Secure.bat
   • %System%Str.vxd
   • %System%Svchost32.exe
   • %System%V32driver.bat
   • %System%Web.swf
     
     Note: %System% is a variable that refers to the System folder. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
     
     
3. Launches%System%Svchost32.exe to hide the mIRC windows running Backdoor.IRC.Zcrew.
   
   
4. Drops the following file:
   
   %Windir%explorer Uninstaller.exe
   
   Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows or C:Winnt.
   
   
5. Drops the following files:
   
   
   • %Windir%WebPrintersimagesBootdrv.dll *
   • %Windir%WebPrintersimagesExplore.dat
   • %Windir%WebPrintersimagesExplore.exe
   • %Windir%WebPrintersimagesExplorer.exe *
   • %Windir%WebPrintersimagesIiscache.dll
   • %Windir%WebPrintersimagesLibparse.exe*
   • %Windir%WebPrintersimagesMoo.dll *
   • %Windir%WebPrintersimagesNavdb.dbx
   • %Windir%WebPrintersimagesPsexec.exe *
   • %Windir%WebPrintersimagesRcfg.ini
   • %Windir%WebPrintersimagesRconnect.conf
   • %Windir%WebPrintersimagesRconnect.exe
   • %Windir%WebPrintersimagesSecure.bat
   • %Windir%WebPrintersimagesStr.vxd
   • %Windir%WebPrintersimagesSvchost32.exe
   • %Windir%WebPrintersimagesV32driver.bat
   • %Windir%WebPrintersimagesWeb.swf
   • %Windir%WebPrintersimagesoywonder.dat
   • %Windir%WebPrintersimagescommands.txt
   • %Windir%WebPrintersimageshidden32.exe
   • %Windir%WebPrintersimagesMdx.dll *
   • %Windir%WebPrintersimagesMoo.dll *
   • %Windir%WebPrintersimagesViews.mdx *
     
     
6. Creates the following folder:
   
   %System%www
   
   
7. Creates the following files:
   
   
   • %System%wwwMdx.dll *
   • %System%wwwMoo.dll *
   • %System%wwwViews.mdx *
     
     Note: All the files marked with an asterisk (*) are parts of commercial programs that this Trojan exploits. They are not malicious in themselves, and as such, Symantec antivirus products do not detect them.
     
     
8. Adds the value:
   
   "ccreg" = "%System%explorer.exe"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the risk runs every time Windows starts.
   
   
9. Adds the value:
   
   "EXPLORE" = "%System%explore.exe"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the risk runs every time Windows starts.
   
   
10. May add the values:
    
    "UninstallString:" = " "c:winntwebprintersimagesexplorer.exe" -uninstall"
    "DisplayName:" = "mIRC"
    
    to the registry subkey:
    
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionUninstallOBCD
    
    
11. May create the following registry subkeys:
    
    HKEY_ALL_USERSSOFTWAREOBCDDateUsed
    HKEY_ALL_USERSSOFTWAREWinRAR SFX
    
    
12. Opens a back door and listens for commands from the remote attacker to execute the following commands:
    
    
    • Create the file, Blah.vbs, to launch a ping flood attack against an IP address
    • Flood UDP packages to an IP address
    • Scan the ports of an infected computer

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 pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Restart the computer in Safe mode.
3. Run a full system scan and delete all the files detected.
4. Delete the value added to the registry.

For specific details on each of these procedures, read the following instructions.

1. 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 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).
• 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).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

2. Restarting the computer in Safe mode
All the Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."

3. 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.
   • 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 that a Symantec Corporate antivirus product is set to scan all files."
2. Run a full system scan.
3. If any files are detected as infected with Backdoor.IRC.Zcrew, click Delete.
4. Using Windows Explorer, locate and delete the folder, %System%www. (All the variants do not add this folder.)
   

4. To delete the value from the registry
Important: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified subkeys only. For instructions refer to the document: How to make a backup of the Windows registry.

1. Click Start > Run.
2. Type regedit
3. Click OK.
   
   Note: If the registry editor fails to open the threat may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.
   
   
4. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
5. In the right pane, delete the value:
   
   "ccreg" = "%System%explorer.exe"
   
   
6. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
7. In the right pane, delete the value:
   
   "EXPLORE" = "%System%explore.exe"
   
   
8. Navigate to and delete the subkeys:
   
   HKEY_ALL_USERSSOFTWAREOBCDDateUsed
   HKEY_ALL_USERSSOFTWAREWinRAR SFX
   
   
9. Exit the Registry Editor.