W32.Downadup Removal

Posted on 8:28 PM by Bharathvn

Discovered: November 21, 2008
Updated: November 24, 2008 9:37:07 AM
Also Known As: Win32/Conficker.A [Computer Associates], W32/Downadup.A [F-Secure], Conficker.A [Panda Software], Net-Worm.Win32.Kido.bt [Kaspersky], WORM_DOWNAD.AP [Trend]
Type: Worm
Infection Length: 62,976 bytes
Systems Affected: Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows Vista, Windows XP
CVE References: CVE-2008-4250
Once executed, the worm copies itself as the following file:
%System%\[RANDOM FILE NAME].dll

Next, the worm deletes any user-created System Restore points.

It creates the following service:
Name: netsvcs
ImagePath: %SystemRoot%\\system32\\svchost.exe -k netsvcs

Then the worm creates the following registry entry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\netsvcs\Parameters\"ServiceDll" = "[PathToWorm]"

The worm connects to the following URLs to obtain IP address of the compromised computer:
  • [http://]www.getmyip.org
  • [http://]getmyip.co.uk
  • [http://]checkip.dyndns.org

Next, the worm downloads a file from the following URL and executes it:

The worm then creates a http server on the compromised computer on a random port, for example:

The worm then sends this URL as part of its payload to remote computers.

Upon successful exploitation, the remote computer will then connect back to this URL and download the worm.

In this way, each exploited computer can spread the worm itself, as opposed to downloading from a predetermined location.

Next, the worm connects to a UPnP router and opens the http port.

It then attempts to locate the network device registered as the Internet gateway on the network and opens the previously mentioned [RANDOM PORT] in order to allow access to the compromised computer from external networks.

The worm then attempts to download a data file from the following URL:

The worm spreads by exploiting the Microsoft Windows Server Service RPC Handling Remote Code Execution Vulnerability (BID 31874).

Next, the worm attempts to contact the following sites to obtain the current date:
  • http://www.w3.org
  • http://www.ask.com
  • http://www.msn.com
  • http://www.yahoo.com
  • http://www.google.com
  • http://www.baidu.com

It uses the date information to generate a list of domain names.

The worm then contacts these domains in an attempt to download additional files onto the compromised computer.


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