After you set up Windows Firewall in Microsoft Windows XP Service Pack 2 (SP2), you may discover that anyone on the Internet can access resources on your computer when you use a dial-up connection to connect to the Internet. For example, after creating an exception in Windows Firewall for File and Printer Sharing, you may discover that anyone can access shared files and printers.

Note Windows Firewall automatically selects the My network (subnet) only scope option when you create an exception for File and Printer Sharing.

Because of the way that some dialing software configures routing tables, Windows Firewall in Windows XP SP2 can sometimes interpret the whole Internet to be a local subnet. This can let anyone on the Internet access a Windows Firewall exception if the exception is configured to use the My network (subnet) only scope option.

Update information

Download information

To resolve this problem, you must download and install critical update 886185. You can download and install critical update 886185 by using the Windows Update Web site or the Microsoft Download Center.

Windows Update

To download and install critical update 886185 by using the Windows Update Web site, follow these steps:

1.	Start Microsoft Internet Explorer.
2.	On the Tools menu, click Windows Update.
3.	Follow the instructions on the screen to update your computer.

Microsoft Download Center

The following file is available for download from the Microsoft Download Center:


Download the critical update 886185 package now. (http://www.microsoft.com/downloads/details.aspx?FamilyId=DA66A0AC-55CA-4591-B3E6-D78695899141&displaylang=en)

Release Date: December 14, 2004

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

Prerequisites

You must be running one of the following operating systems:

•	Microsoft Windows XP Service Pack 2
•	Microsoft Windows XP Media Center Edition with Windows XP Service Pack 2
•	Microsoft Windows XP Tablet PC Edition 2005

Deployment information

To install critical update 886185 without any user intervention, use the following command:
To install this critical update without forcing the computer to restart, use the following command: Note You can combine these switches in one command line. For additional information about the command-line switches that can be used with critical update 886185, click the following article number to view the article in the Microsoft Knowledge Base: For information about how to deploy this critical update by using Software Update Services (SUS), visit the following Microsoft Web site:

Removal information

To remove this critical update, use the Add or Remove Programs tool in Control Panel.

System administrators can use the Spuninst.exe utility to remove this critical update. Spuninst.exe is located in the %windir%\$NTUninstallKB886185$\Spuninst folder. The utility supports the following Setup switches:

•	/? : Show the list of installation switches.
•	/u : Use Unattended mode.
•	/f : Force other programs to quit when the computer shuts down.
•	/z : Do not restart when the installation is completed.
•	/q : Use Quiet mode (no user interaction).

Restart requirement

You may have to restart your computer after you apply this update.

Update replacement information

This update does not replace any other updates.

File information

The English version of this update has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Date	Time	Version	Size	File name	Folder
29-Sep-2004	22:28	5.1.2600.2524	134,912	Ipnat.sys	SP2GDR
29-Sep-2004	22:31	5.1.2600.2524	134,912	Ipnat.sys	SP2QFE

For additional information about Windows XP Service Pack 2 software update packages, click the following article number to view the article in the Microsoft Knowledge Base:

Some dial-up software configures the routing tables in a way that leads the Windows Firewall to determine that the whole dial-up connection is on the local subnet. After you install critical update 886185, Windows Firewall will no longer interpret network connections to be on the local subnet if they have IP Route Table entries that have an IP address of 0.0.0.0 and a mask of 0.0.0.0. This means that any port exceptions or program exceptions that use the My network (subnet) only scope option in Windows Firewall will not be available over most dial-up connections. You will still be able to access exceptions over a dial-up connection if you remove all scope restrictions or if you create a custom scope for exceptions.

Local network subnet configuration varies depending on the network that you are connected to and how that network is configured. Using the My network (subnet) only scope restriction does not guarantee security because it relies on the network subnet configuration to define what is the local network.

Important We strongly recommend that you use the custom scope option when you want to make sure that no unwanted incoming traffic is permitted to pass through your firewall exceptions.

To access the custom scope options for an exception, follow these steps:

1.	Log on to your computer as a member of the local Administrators group.
2.	Click Start, click Run, type firewall.cpl, and then click OK.
3.	In Windows Firewall, click the Exceptions tab. Click the program or service that you want to create an exception for.
4.	Click Edit, click Change scope, and then click Custom list.

For more information about configuring Windows Firewall, visit the following Microsoft TechNet Web page: