Another IE 5 security flaw found

Microsoft might consider putting Bulgarian programmer Georgi Guninski on the payroll. The software maker has acknowledged that Guninski discovered yet a third security flaw in Internet Explorer 5 browser software.

The latest flaw, under certain circumstances, would allow a Web site operator to access and read contents of files and folders on the computers of users, Microsoft said in a security bulletin posted online Monday. The Web site operator would have to know the name of the file and the folder in which it was located in order to access it, and would not be able to list folder contents or create, modify or delete files, according to Microsoft.

The company is working on a patch for the flaw, but in the meantime is suggesting that users disable active scripting in the Internet zone, an IE security zone in which all Internet Web sites are automatically categorised.

IE 5 restricts the actions that a Web site can take on computers of visitors. "When software on the Web server requests that particular action be taken on a visiting computer, IE examines it and only allows the request to be made if it's appropriate. However, not all of the checks are present if the requesting software lies within an IFRAME. Specifically, certain requests that are made via a scripting method called ExecCommand() are not properly bounded if invoked on an IFRAME," according to a question-and-answer section about the latest flaw posted on the Microsoft Web site.

An IFRAME is a sub window within the main browser window, and is viewed by the software running in it as its own window, working separately from the main window, Microsoft said.

To disable active scripting in the Internet zone, users should:

-- While in IE 5, select "tools," then "Internet options." Click on the "security" tab.

-- Go to the box labelled "select a Web content zone to specify its current security settings" and click on "Internet" and then "custom level."

-- Scroll down to "scripting," which is a major heading and then locate the minor heading called "active scripting." Click the "disabled" button under "active scripting."

-- Click twice on "OK" to accept the changes.

Users also are being encouraged by Microsoft to add Web sites to the security zone called the Trusted Zone, containing sites that users trust will not take malicious action against user computers.

Additional information about the flaw can be found at http://www.microsoft.com/security/bulletins/MS99-042faq.asp or at http://www.microsoft.com/security/default.asp.

The security bulletin from Microsoft acknowledges Guninski's role in bringing the problem to light.

Last month, he was credited for finding the second security flaw he has uncovered in IE 5. That flaw could allow a malicious Web site operator to read files on user computers or on other computers in the user's local intranet. The flaw was found in the "download behavior" feature of IE 5.

A Microsoft spokesman could not be reached to comment about the latest flaw or to provide information about whether any Web users appear to have used the bug to access data on users' computers.

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Nancy Weil

PC World
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