Attackers Targeting Zero-Day Access Flaw

Attackers are going after Microsoft Office Access databases, US-CERT warned earlier in the week, taking advantage of an unpatched stack buffer overflow to deliver malicious databases that are leading to system hijacking in an undetermined number of cases.

Security researchers didn't have many details on the attacks, but US-CERT's advisory did say that users don't have to do anything beyond open a rigged Access database in order for a successful exploit to be sprung on them. The malicious files are of file type .MDB.

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McAfee's Avert Labs said in a Dec. 12 posting that attacks could come via a number of vectors: via the Web, e-mail or instant messaging, "coupled with well-establishing social engineering techniques" to trick victims into launching an attachment that's been booby trapped.

US-CERT is recommending that, in lieu of a patch, users take these mitigation steps:

• Avoid opening attachments from people they don't know or trust or that they haven't solicited.
  
• Block high-risk file attachments at e-mail gateways.

Microsoft Director of Security Response Mark Miller said in a statement that, "Microsoft is aware of public reports of a malicious Microsoft Access Database file being used to compromise users," though he didn't provide information on how widespread the attack is at this point.

The file type in question—.MDB—is considered unsafe, Miller noted, since it's one of multiple file types that allow embedded script operations. Macros in Word files (*.doc) or in Excel files (*.xls) are other examples of file types that can be risky because of their less-than-obvious leniency on embedded scripts, according to this Microsoft support page on unsafe file types.

.MDB was used by Access Database versions up until 2003 and is either blocked by some Microsoft applications or provokes warnings before users can open such files, Miller said in his statement.

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