Microsoft released another cumulative patch for Internet Explorer yesterday, which promises to plug up six recently discovered security defects involving the browser.
The patch, for IE 5.01, 5.5 and 6.0, includes the functionality of previously released fixes, as well as tackling the new problems - the most serious of which could allow an attacker to run code of his choice on a victim's machine. Microsoft describes the patch as 'critical', so let's hope it works properly.
Six of the worst
The most serious bug involves a cross-site scripting vulnerability. IE ships with several files that contain HTML on the local file system, one of which contains a flaw that could allow a script to execute as if it were run by the user. This bug could be exploited by an attacker who tricks victims into either visiting a maliciously constructed Web page or opening HTML email containing a poisoned script.
Next up us is an information disclosure vulnerability related to a buggy HTML object, which is designed to provide support for Cascading Style Sheets. Because of the bug, an attacker might be able to read, but not delete or change, data on a local system, MS says.
Moving on, there's an information disclosure vulnerability involving to the handling of script within cookies, which could potentially allow one site to read the cookies of another.
Then there's a zone spoofing vulnerability that could allow a Web page to be incorrectly reckoned to be in the Intranet zone or, in some very rare cases, in the Trusted Sites zone.
Finally there are two variants of a 'content disposition' vulnerability, which relate to how IE handles downloads when a downloadable file's Content-Disposition and Content-Type headers are intentionally malformed. Virus writers might use the technique to disguise the fact that an attachment contains executable content, hence the need for the patch.
As well as plugging up the six vulnerabilities listed above, Microsoft's patch also disables frames in the Restricted Sites zone. The change means that recently released MS email clients (and those with Outlook Email Security Update installed) will disable frames in HTML email by default, blocking the possibility of an HTML email automatically opening a new window or launching the download of an executable. At least that's the idea.
You could read about the problems in more details, and get links to the relevant patch, in Microsoft's advisory on the subject. ®