"For users of Office prior to 2010, the Enhanced Mitigation Experience Toolkit (EMET) can help," said Andrew Roths and Chengyun Chu, a manager and security engineer respectively with the Microsoft Security Response Center (MSRC). "Turning on EMET for the core Office applications will enable a number of security protections called 'security mitigations'," the pair wrote in a post to the company's Security Research & Defense blog.
EMET is a tool designed for advanced users, primarily enterprise IT pros, that manually enables ASLR (address space layout randomisation) and DEP (data execution prevention) for specific applications. ASLR and DEP are two anti-exploit technologies included with Windows.
Last weel, Adobe confirmed that attackers were exploiting an unpatched bug in Flash Player by sending potential victims malicious Microsoft Excel documents.
Excel is the spreadsheet bundled with the Office suite.
According to Roths and Chu, Excel 2010, the version included with Office 2010, is not susceptible to the attacks now in circulation because that edition of the spreadsheet has DEP enabled. "The current attacks do not bypass DEP," they said.
Excel 2010 further protects users by isolating malicious files inside Office 2010's 'Protected View', a 'sandbox' that prevents attack code from escaping the application.
But people running older versions of Excel - including the versions in Office 2007 and 2003 - are not protected by DEP or Protected View.
Microsoft has recommended EMET before as a stop-gap defence when Adobe zero-days have hit the street. In September 2010, Microsoft told users to configure EMET to block attacks exploiting a then-unfixed flaw in Adobe Reader.
EMET 2.0 is a free download available from Microsoft's site. After downloading and installing EMET, users must manually configure the tool to add protection to Office's applications, Excel included, and perhaps their browser(s) as well.
Adobe plans to patch the Flash Player vulnerability sometime this week.