Thursday, October 1, 2009

Control malicious apps with DEP in IE

DEP helps block malware in Internet Explorer

Internet Explorer 8 includes a security feature that shuts down misbehaving applications before they can harm your system. This capability, known as Data Execution Prevention (DEP), runs by default when IE 8 is installed on XP SP3 and Vista SP1 or later, but it may not always be clear to you why DEP has put the brakes on one of your PC's applications.

DEP is the best reason I know for updating to Internet Explorer 8 and Vista SP1. For many years, Microsoft has included DEP — which is also called No-Execute (NX) — only in parts of Windows. For example, DEP is available in IE 7 but is off by default to avoid conflicts with old, incompatible programs.DEP is now a key part of Vista and Internet Explorer 8. When I try to install older software on newer machines, I must configure Data Execution Prevention to allow the software installer to run with DEP disabled.

To open the Data Execution Prevention dialog in XP, open Control Panel, choose System, and then select the Advanced tab. Click the Settings button in the Performance section and select the Data Execution Prevention tab. In Vista, choose Performance Information and Tools, click Advanced Tools in the left pane, select Adjust the appearance and performance of Windows, and click the Data Execution Prevention tab.

For instance, when I install QuickBooks 2007 on Windows Server 2008, I have to exclude under the DEP tab the QuickBooks updating tool in order to install it on the server. Keep in mind that the only reason I'm doing so is because I trust Intuit, the publisher of QuickBooks. If I didn't change the settings, DEP would prevent me from installing an older version of this software on the newer system.
If I didn't already trust the vendor, I'd look for valid reasons why DEP was blocking the installation before I took the step of changing any DEP settings. In most instances, good, up-to-date software shouldn't need to be excluded from DEP.

Since IE 7, Microsoft has used DEP to help thwart online attacks in the browser itself. What the company didn't do until IE 8, though, was to enable DEP by default. Prior to IE 8, DEP was disabled by default for compatibility reasons, as documented on the IE blog. Many older IE add-ons were built using earlier versions of the Active Template Libraries (ATL). They aren't compatible with DEP, therefore, and crash when IE loads them.

When DEP is enabled and combined with Address Space Layout Randomization (ASLR), IE's ability to protect against Web-based attacks improves considerably. In a nutshell, ASLR is designed to make it harder for automatic attacks to occur. You can read more about ASLR in the MSDN blog.

Specifically, ASLR helps prevent exploits both in IE and in any add-ons that are loaded. Even with the new security protections in IE 7 and 8, the browser is still targeted more often by malware authors than other browsers. This has caused security pundits to state, as Wired's Brian X. Chen does on the Gadget Lab blog, that Apple's new Snow Leopard operating system is "less secure than Windows, but safer."

(If you use Snow Leopard, I encourage you to update your system to OS X version 10.6.1. This includes a patch for the insecure Adobe Flash Player that Snow Leopard shipped with, as documented in an Apple security update.)

There are many protections built into Internet Explorer 8 that may be considered just another annoying browser crash when seen in action.

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