Microsoft said it was investigating reports of "very limited, targeted attacks using a vulnerability in the Microsoft Jet Database Engine that can be exploited through Microsoft Word."
The Microsoft Jet Database Engine extends data access to a variety of Microsoft and third-party applications, including Microsoft Access, Microsoft Visual Basic, and certain Information Services (IIS) applications.
Versions of the Microsoft Jet Database Engine (msjet40.dll) lower than 4.0.9505.0 are vulnerable to a buffer overrun flaw. For the attack to succeed, an attacker would have to convince a user to open a Word file, either as an attachment or hosted on a Web site, designed to load a database file that uses msjet40.dll.
Microsoft considers the risk to be "limited." It advises users of its software not to open Word documents from untrusted sources or unexpected Word documents from anyone.
A variety of security vendors have noted that targeted attacks have become more prevalent in recent years. Because they affect only a few organizations or individuals, targeted attacks tend to elicit less of a response from technology providers and law enforcement.
The vulnerability affects Microsoft customers running Microsoft Word 2000 Service Pack 3, Microsoft Word 2002 Service Pack 3, Microsoft Word 2003 Service Pack 2, Microsoft Word 2003 Service Pack 3, Microsoft Word 2007, and Microsoft Word 2007 Service Pack 1 on Microsoft Windows 2000, Windows XP, or Windows Server 2003 Service Pack 1.
Users of Windows Server 2003 Service Pack 2, Windows Vista, and Windows Vista Service Pack 1 are not vulnerable.
Earlier this month, as part of its regularly scheduled Patch Tuesday, Microsoft fixed a dozen vulnerabilities in its Office suite. Eric Schultze, chief technology officer of Shavlik Technologies, said at the time that vulnerability fixes in client-side applications follow from attackers looking more closely at server-side vulnerabilities.