Tip

Security breaches

Security breaches

Today's tip comes to us from, Tertius Genis, who works for Weyerhaeuser Corp.

The tip discusses one way that security breaches can happen through the page file -- and how to avoid them. The page file, a hidden file called pagefile.sys, is the one your computer uses to page out programs and/or data to hard disk when memory resources are getting low. It's the same thing as the swap file in Unix. When you install Windows 2000, the installation program sets the size of the swap file to 1.5 times more than you have physical memory in your machine. For example, a 250 MB machine would have a default swap file size of 775 MB.

But the page file leads to a serious problem. A few of the attacks on Windows NT Security about which information is publicly available rely on the fact that the NT page file is left intact on shutdown and can subsequently be scanned for useful information. There's no good reason that the page file isn't erased, and doing so can plug a potential hole in your NT or Windows 2000 armor.

To clear the page file at shutdown, you need to change the registry. Make sure you back up the registry prior to implementing the change, so if you mess up, you can go back to where you were.

Change the following key in the registry:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSession
ManagerMemory
ManagementClearPageFileAtShutdown

Drill down to the key, and set the value in the dialog box that appears when you double-click on it. To have the file cleared at shutdown, set the value of the key to 1. To leave the page file intact at shutdown, set the value to 0.


This was first published in October 2000

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