Latest SP2 Flaw Bypasses IE Security Zone

By Larry Seltzer  |  Posted 2004-08-21 Print this article Print

A researcher is able to execute scripting in Internet Explorer's local computer zone, contrary to Service Pack 2 restrictions.

Security researchers have discovered another vulnerability in Windows XP Service Pack 2, but it doesnt appear to be an immediate threat. The researcher who uncovered the drag-and-drop flaw in Windows XP SP2 earlier in the week has reported that a new vulnerability exposes a hole in the lockdown of Internet Explorers My Computer security zone.

The lockdown of the My Computer zone is one of the major security enhancements in SP2. Web pages in Internet Explorer run in one of several security "zones," each of which has different security rules. Prior to SP2, the My Computer zone—designed for Web pages stored on the computer itself—had extremely permissive rules. In order to take advantage of them, malware attacks frequently exploited vulnerabilities to get their Web-based pages to execute. Microsoft tightened the rules in SP2 to make it a less inviting target.

In the new attack, the use of an unconventional value in the "Content-Location:" field of an MHTML (MIME HTML) file causes the browser to execute the file in the Local Intranet zone, even though it is run from the local computer. This allows scripting operations that are not permitted in the local zone. MHTML files are a variant HTML format in which accessory files, such as images, can be stored as part of the file itself.

While this example does demonstrate a weakness in the local computer lockdown by Service Pack 2, the technique doesnt work in a standard HTML file delivered in a browser. Because the file must be downloaded by the user and executed locally, it is much harder to deliver to the user. It is, in a sense, no different from a threatening .exe file. It is possible that it could be blended in the future with other exploits of SP2 to create a true remote attack.

Check out eWEEK.coms Security Center for the latest security news, reviews and analysis. And for insights on security coverage around the Web, take a look at Security Center Editor Larry Seltzers Weblog.

Be sure to add our developer and Web services news feed to your RSS newsreader or My Yahoo page

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

Submit a Comment

Loading Comments...
Manage your Newsletters: Login   Register My Newsletters

Rocket Fuel