January 11, 2006
Microsoft's Newest Bug Could Be Awful, Researcher Says
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The Outlook and Exchange vulnerability
disclosed by Microsoft Tuesday has the potential to become a much more virulent problem than the long-hyped
Windows Metafile bug patched last week, said one of the e-mail flaw's discoverers Wednesday.
"What I find bizarre is that there's still all this focus on the WMF [Windows Metafile] bug," said Mark Litchfield, the director of NGS Software, a U.K.-based security company, and one of the two researchers credited by Microsoft with the discovery of the TNEF (Transport Neutral Encapsulation Format) vulnerability.
"This one has massive financial implications if someone exploits it," Litchfield said.
The TNEF vulnerability, which Microsoft spelled out in the MS06-003 security bulletin, is a flaw in how Microsoft's Outlook client and older versions of its Exchange server software decode the TNEF MIME attachment. TNEF is used by Exchange and Outlook when sending and processing messages formatted as Rich Text Format (RTF), one of the formatting choices available to Outlook users.
"All that's required to exploit this is an e-mail message," said Litchfield. No user interaction is needed to compromise an Exchange 5.0, 5.5, or 2000 server; all that's necessary is to deliver a maliciously-crafted e-mail to the server.
It's that characteristic, as well as the ease with which an attack could spread, that has Litchfield so worried.
"You could take over an Exchange server with a single, simple e-mail," he said. "From there you could target all the clients accessing that server. You would 'own' any Outlook client that connects to that server. Then an attacker could grab the Outlook users' address books.
"If you did it right, you could own every Outlook user in the world within a week," he said.
Microsoft noted the severity of the bug by tagging it with its highest warning label, "Critical," and by providing a patch for Exchange 5.0 and 5.5, obsolete versions whose support technically ended Dec. 31, 2005. The newest server software, Exchange Server 2003, is immune to the bug, although current editions of Outlook, including Outlook 2003, are not.
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