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A trio of MS-Office security vulns

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Researchers at GreyMagic Software have uncovered three novel vulnerabilities provided by Microsoft Office Web Components (OWC), which can override security settings in Internet Explorer.

First up, it's possible, using the spreadsheet component of OWC, to enable active scripting when the user has it disabled in IE.

"One of the features added to the spreadsheet component is the '=HOST()' formula, which returns a handle to the hosting environment.

"It is possible to use this formula in order to manipulate the DOM [the Document Object Model, which allows scripts to access and alter documents], which is a security issue in itself when Active Scripting is disabled, but it's somewhat limited because there's no way to add logic (conditions, loops, etc.) to the calls made.

"However, with a bit of manipulation it is possible to get Active Scripting to kick in. By using the setTimeout method of the window object through the '=HOST()' formula it is possible to execute script with any language available to the host," GreyMagic says.

The workaround for now is to disable not just active scripting but ActiveX and plugins as well. There is a sample script and two demonstrations linked at the bottom of the GMS bulletin here, one of which enables the curious to try out their own scripts quite conveniently.

Next, the spreadsheet component also enables an attacker to control the clipboard even when the IE option "allow paste operations via script" has been disabled.

"The 'Paste' method of the Range object and the 'Copy' method of the Cell object give an attacker full control over clipboard operations," GreyMagic says.

In this case control means just what it says: the ability to read from and insert data into the victim's clipboard. There are three sample scripts posted with the bulletin, along with a demonstration. The workaround, again, is to disable ActiveX and plugins until MS issues a fix.

Finally, it is possible to read local files, again by exploiting the spreadsheet component.

"The 'LoadText' method of the Range object takes a URL as its first argument; it throws an error if the URL supplied is not in the same domain as the current document.

However, this protection can be easily bypassed by supplying a URL that will redirect to the desired local or remote file.

OWC is fooled to think that the URL is safe and loads the contents of the file into the spreadsheet; it is then trivial to retrieve the content and transfer it to the server or use it in malicious ways," GreyMagic says.

The associated advisory includes two sample scripts and a demo. Once again, the workaround is to disable ActiveX and plugins.

According to GreyMagic, MS has been notified of all the above difficulties and is currently investigating them. No doubt Redmond will be much irritated by disclosure ahead of their patch release; but since there are effective workarounds, it seems better that users should be informed and given the chance to take immediate steps rather than be kept ignorant and vulnerable.

Anyone who wishes to retain the use of plugins can of course download Mozilla, a free version of Netscape that runs quite nicely, and safely, on Windows. ®

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