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Microsoft released three software patches rated "critical" late Thursday. The patches plug holes in Internet Explorer, Windows XP, SQL Server 2000, and Commerce Server 2000.

Two of the patches aim to fix information disclosure flaws in Microsoft's Web browser Internet Explorer.

The first flaw exists in IE versions 5.01, 5.5, and 6.0. Through it, malicious Web site operators can read files on users' computers and tap information entered into the Web browser such as usernames, passwords, and credit card details, Microsoft says in security bulletin MS02-009.

The problem lies in the way IE handles scripting across domains within frames, Microsoft says. The flaw allows VBScript, Microsoft's script language, running in one domain--the domain of the attacker--to read data in a frame belonging to another domain, which could be the user's local PC or an online shop.

To be exposed to this VBScript handling flaw, a user would have to go to a Web site that is under the attacker's control or open an HTML e-mail from the attacker, Microsoft says. The patch fixes the vulnerability by instituting domain verification handling for VBScript.

Reading Files

The second information disclosure flaw also requires a user to visit an attacker's Web site and would allow the attacker to read files on users' systems, Microsoft says in security bulletin MS02-008.

This flaw requires patching of Internet Explorer 6.0, the operating system Windows XP and database server SQL Server 2000, as these applications all contain the flawed code.

This vulnerability, dubbed the XMLHTTP bug by security experts because it appears in the XMLHTTP ActiveX control, has been waiting for a plug since it was published on December 15 last year.

The ActiveX control is part of Microsoft's XML Core Services software. Flawed versions of the control ship as part of Windows XP, IE 6.0, and SQL Server 2000. They do not respect the security zone settings in IE, allowing a Web page to specify a file on a user's computer as an XML data source as a means of reading the file, Microsoft says. XML Core Services software is used by other applications to parse, generate, validate, and transform XML documents so that the information can be displayed, stored, or manipulated, Microsoft says.

Internal Review

The third patch Microsoft issued is to fix a buffer overrun flaw in Commerce Server 2000, software that supports electronic commerce Web sites. The flaw was discovered as part of Microsoft's internal security code review, the company says. An attacker exploiting the flaw could gain full control over the system running the software by sending a malformed request to it, Microsoft says in security bulletin MS02-010.

The flaw lies in a software component called AuthFilter, an Internet Services Application Programming Interface filter that provides support for authentication methods on the system. This filter is installed by default, Microsoft says. All administrators using Commerce Server 2000 are urged to patch their systems.

Installing URLscan, a software tool recommended by Microsoft, will protect Commerce Server 2000 installations from being taken over by an attacker, but the server can still be caused to fail by sending it a malformed request, Microsoft notes. Earlier versions of the software, including Site Server 3.0 and Site Server 3.0 Commerce Edition, are not affected, the software maker says.

Thor Larholm, a Danish Internet programmer and security expert who maintains a list of security holes Microsoft has yet to patch on his Web site, says Microsoft is on the right track.

"It is nice to see that they have patched most of the holes listed on my site, but it is frightening to witness the amount of time it took and the pressure from the public that was needed," he says. "However, Microsoft's actions are a promising trend and I hope their initiative to put more focus on security will outlive the month."

Taking a Break

Microsoft has announced it will take a break of about a month from developing new code to go back to the already written software and check that for security flaws. The now-patched Commerce Server 2000 flaw seems to be the first result of those efforts.

"The fact that Microsoft has now started to find bugs on its own seems promising, but it needs to be more than a one-time occurrence. Microsoft needs to rethink fundamental parts of its security processes, as it is too easy for outsiders, with no access to Microsoft's closed source, to find new security holes," Larholm says.

Notwithstanding the patches, IE remains vulnerable, according to Larholm.

"Internet Explorer remains insecure. In the next month or two we will probably have about five new vulnerabilities. I have listed three current vulnerabilities that aren't public yet, but were discovered by a software firm. Microsoft is currently investigating these holes that allow an attacker to read local files," he says.

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