Zero Day

Details, details, details... more on the Microsoft flaws from today

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Microsoft
Patch Watch

Thought I'd explore some of these bugs a bit more... first, Tipping Point released one of the vulnerabilities that Larry reported earlier, listed as a stack overflow issue in Microsoft Office Jet Database Engine. The stack overflow isn't what's interesting, what's interesting is the attack vector itself. To be fair to Microsoft, if someone dropped an MDB file on me and said that it would cause a stack overflow, I probably wouldn't consider it to high a priority, as running an MDB on your system is akin to running an executable; however, in this case, the MDB was actually embedded into a word document... hmm much more interesting! This makes me want to consider other Jet database engine flaws. Here's the details from Tipping Point:

TPTI-08-04: Microsoft Office Jet Database Engine Column Parsing Stack Overflow Vulnerability Also listed as: CVE-2007-6026 -- Vulnerability Details: This vulnerability allows remote attackers to execute arbitrary code on vulnerable installations of Microsoft Office. Exploitation requires that the target opens an Office file that contains malicious Jet DB Engine objects. The specific flaw exists within the parsing of a column structure. The DWORD value from the structure that specifies the column count is trusted. If this value is changed, an inline memcpy to the stack can overflow while reading a column name. Typically Jet DB structures are used within MDB files which are considered unsafe. However, it is possible to embed such files within a trusted format, such as an Office Document (.doc). This issue allows for remote code execution under the context of the currently logged in user.

The second that's interesting to review is from iDefense and is listed as MS08-026. It's a flaw in Word's ability to process an overly large number of CSS selectors, which results in an unspecified object being corrupted, causing Word to access a memory region that has already been freed. What I think is most interesting about this is that the attack leverages Word's processing of HTML... this is an interesting place to attack. Think about it, a lot of the functionality of a browser, but instead, it's in Word. Here's the details from iDefense:

Remote exploitation of a memory corruption vulnerability in Microsoft Corp.'s Word could allow attackers to execute arbitrary code with the privileges of the logged in user. This vulnerability exists in the way Word handles CSS rules in an HTML document. When the number of CSS selectors is above some specific amount, an unspecified object will be corrupted causing Word to access a memory region that has already been freed.

I'm not sure if iDefense has worked up exploit code for this, but that would certainly be interesting to see. -Nate

posted by Nathan McFeters
May 13, 2008 @ 1:40 pm

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