Microsoft Warns of MHTML Bug in Windows

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Microsoft Warns of MHTML Bug in Windows

Microsoft is warning its users about a dangerous flaw in the way that Windows handles certain MHTML operations, which could allow an attacker to run code on vulnerable machines. The bug affects all of the current versions of Windows, from XP up through Windows 7 and Windows Server 2008.

Microsoft issued an advisory about the MHTML vulnerability, which has been discussed among security researchers in recent days. There is some exploit code available for the bug, as well. In addition to the advisory, Microsoft has released a FixIt tool, which helps mitigate attacks against the vulnerability in Windows.

Following the advisory advice, fix is to simply disable MHTML for now, MS have released a tool available @ http://support.microsoft.com/kb/2501696

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The vulnerability exists due to the way MHTML interprets MIME-formatted requests for content blocks within a document. It is possible under certain conditions for this vulnerability to allow an attacker to inject a client-side script in the response of a Web request run in the context of the victim's Internet Explorer. The script could spoof content, disclose information, or take any action that the user could take on the affected Web site on behalf of the targeted user.

Possibly IE only, unconfirmed.

We are collaborating with Service Providers to investigate server-side workarounds, but we recommend that customers apply one or more of the client-side workarounds provided in the Suggested Actions section of this advisory to help block potential attack vectors regardless of the service.

So it's not being taken lightly.