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Microsoft Warns of Another Server Message Block Bug

The all-critical patch release of hotfixes served up by Redmond Tuesday hadn't even cooled off yet when Microsoft issued yet another security advisory on late Tuesday night.

This time the flash advisory is for potential vulnerabilities in Microsoft's Server Message Block (SMB). The advisory describes SMB as a "network file sharing protocol used in Microsoft Windows." The company is currently preparing a security update for future release.

According to the advisory, Microsoft is looking into "new public reports of a possible vulnerability in SMB implementation" affecting Windows Vista, Windows Server 2008 and the Windows 7 release candidate.

Windows 7 and Windows Server 2008 R2 are not affected, nor are Windows XP and Windows 2000.

Redmond said that it is "not aware of attacks that try to use the reported vulnerabilities," nor has it received any direct customer complaints about the issue.

The off-cycle advisory -- the second in as many weeks -- comes on the same day after Microsoft's September patch was made available. That patch addressed five "critical" security issues associated with Web components in Windows and other Microsoft software. Microsoft has also given notice of another yet-to-be fixed bug in a File Transfer Protocol (FTP) component.

SMB is used for client-server traffic handling, and Microsoft's security advisory recommends a workaround that involves modifying the Windows registry and "blocking TCP ports 139 and 445 at the firewall."

SMB bugs have been seen before. In November of 2008, Redmond confirmed that it took seven years to deliver a fix for SMBRelay attacks. That fix finally arrived in Microsoft's November's patch. At the time, Microsoft Security Response Center spokesperson Christopher Budd admitted in a blog post that Microsoft's security staff was unable to "make changes to address the issue without negatively impacting [other] network-based applications."

Independent security researcher Laurent Gaffié apparently broke the news about the SMB vulnerability on Tuesday night in his blog and then contacted Microsoft about the issue. Redmond apparently wasn't pleased.

"Microsoft is concerned that this new report of a vulnerability was not responsibly disclosed, potentially putting computer users at risk," the security advisory said. "We continue to encourage responsible disclosure of vulnerabilities."

Microsoft said it is working with partners in its Microsoft Active Protections Program on the issue.

About the Author

Jabulani Leffall is an award-winning journalist whose work has appeared in the Financial Times of London, Investor's Business Daily, The Economist and CFO Magazine, among others.

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