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[ISN] Microsoft confirms Excel bug, hacks; recommends blocking files
By Gregg Keizer
January 16, 2008
Ongoing attacks are exploiting a flaw in most versions of the popular
Excel spreadsheet application, Microsoft Corp.'s security group said
The attacks, which the Microsoft Security Response Center (MSRC)
downplayed as "targeted, and not widespread," are using a bug found in
Excel 2000, Excel 2002, Excel 2003 Service Pack 2, Excel Viewer 2003 and
Excel 2004 for Mac. Newer editions -- Excel 2003 SP3, Excel 2007 and
Excel 2008 for Mac -- are not vulnerable, Microsoft claimed. That last
version, Excel 2008 for Mac, launched earlier Tuesday at the Macworld
Conference & Expo in San Francisco.
"Microsoft is aware of specific targeted attacks that attempt to use
this vulnerability," said Tim Rains, the security response
communications lead at Microsoft, in an e-mail forwarded by the
company's public relation firm. "Microsoft is aggressively investigating
the public reports and customer impact."
According to the security advisory Microsoft posted Tuesday night, the
vulnerability -- which it did not specify -- could let attackers jimmy a
PC sufficiently to snatch control from the rightful owner.
The likely attack vectors, said the advisory, would be to attach a
malformed document to e-mail or stick it on a Web site, then convince
users to open the file.
Office file format vulnerabilities, even vulnerabilities specifically
within Excel, are not new. Attackers have uncovered -- and used -- a
wide array of bugs in Word, Excel and PowerPoint documents for nearly
two years, often in pinpoint attacks that seed a very small number of
businesspeople with spam that includes attached files.
In lieu of a patch -- which Microsoft did not promise it would produce
-- the company recommended that Office 2003 users run suspect Excel
files through MOICE (Microsoft Office Isolated Conversion Environment),
a free conversion tool released last year that converts Office 2003
format documents into the more secure Office 2007 formats to strip out
possible exploit code. Alternately, it told administrators they could
block all Office 2003 and earlier formats except those in "trusted
locations" by using File Block, a last-ditch defense that requires
editing the Windows registry or modifying Group Policy settings.
Ironically, file blocking -- albeit enabled by default first in Office
2007, then in September's Office 2003 SP3 update -- has raised a minor
ruckus in the past week as users complained of the practice, and
Microsoft tried to calm the waters by making it slightly easier to
unblock the older, but banned, formats.
The last time that Microsoft patched any edition of Excel was in August
2007, when it issued MS07-044, an update that fixed a similar document
format flaw in Excel 2000, Excel 2002, Excel 2003 and Excel 2004 for
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