W32.HLLW.Gaobot.gen

1. Copies itself to the %System% folder. The file names vary and are often selected to resemble the names of legitimate Windows system files. Some examples include Csrrs.exe, Scvhost.exe, System.exe, explored.exe, or lms.exe.
   
   However, many other file names have been seen. The attacker can program the file names and the actions that the worm performs.
   
   

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   Note: %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

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2. Adds a value in the form:
   
   "<key name>" = "<the filename of the worm>"
   
   for example:
   
   • "Configuration Loader" = "Service.exe"
   • "Windows Login" = "lms.exe"
     
     to the registry keys:
     
   • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\
     RunServices
     
     so that the worm runs when you start Windows.
     
     
3. May create a service for the worm and set it to automatically run on startup. To do this, the worm creates a registry key:
   
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\<service name>
   
   

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   Note: Typical values for <service name> are x4, a3, or MpR. However, the name can be configured to be any value.

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4. Connects to an IRC server, using its own IRC client, and then listens for commands to do any of the following:
   
   • Download and execute files
   • Steal system information
   • Send the worm to other IRC users
   • Add new accounts
   • Perform Denial of Service (DoS) attacks
     
     
5. Attempts to spread to other computers using numerous vulnerabilities. These could include:
   
   • The DCOM RPC vulnerability (described in Microsoft Security Bulletin MS03-026) using TCP port 135.
   • The WebDav vulnerability (described in Microsoft Security Bulletin MS03-007) using TCP port 80.
   • The Workstation service buffer overrun vulnerability (described in Microsoft Security Bulletin MS03-049) using TCP port 445. Windows XP users are protected against this vulnerability if Microsoft Security Bulletin MS03-043 has been applied. Windows 2000 users must apply MS03-049.
   • The Microsoft Messenger Service Buffer Overrun Vulnerability (described in Microsoft Security Bulletin MS03-043).
   • The Locator service vulnerability (described in Microsoft Security Bulletin MS03-001) using TCP port 445. The worm specifically targets Windows 2000 machines using this exploit.
   • The UPnP vulnerability (described in Microsoft Security Bulletin MS01-059).
   • The vulnerabilities in the Microsoft SQL Server 2000 or MSDE 2000 audit (described in Microsoft Security Bulletin MS02-061), using UDP port 1434.
   • The LSASS vulnerability (described in Microsoft Security Bulletin MS04-011) using TCP ports 139 and 445.
   • The backdoor ports that the Beagle and Mydoom families of worm open.
     
     
6. Attempts to connect to network shares. To do this, it uses easily guessed user name/password combinations, including empty passwords.
   
   Some examples of this are:
   
   • admin$
   • c$
   • d$
   • e$
   • print$
     
     
     Read the W32.HLLW.Gaobot.AA writeup for a sample list of user names and passwords.
     
     
7. Copies itself to any computers that it compromised using the previously mentioned exploits.
   
   
8. Remotely schedules a task to run the worm on a newly infected computer.
   
   
9. Queries the registry to steal the CD keys of various games.
   
   
10. Terminates antivirus and firewall software, as well as the process names associated with other worms.
    
    
11. Recent Gaobot variants may add entries to the %System%\drivers\etc\hosts file to disable access to certain antivirus Web sites.
    
    Refer to the W32.Gaobot.ZW writeup for a typical list of entries that may be added to the Hosts file.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
• 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.
• Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
• Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
• Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
• Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
• If a 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate compromised computers quickly to prevent threats from spreading further. 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.
• If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
• For further information on the terms used in this document, please refer to the Security Response glossary.