'Silent' Fix For Windows USB Bug?

Among the three zero-day vulnerabilities in the 24 software flaws patched by Microsoft this week was a security update for a USB attack affecting older versions of Windows.

The elevation of privilege vulnerability (MS14-063) in Windows Server 2003 and 2008 and Vista is in the FASTFAT system driver of these operating systems, which manages the FAT32 file system that handles the reading and writing of data from a disk. A Cisco researcher reported to Microsoft the bug in the older Windows OSes.

Researchers at BeyondTrust were curious why newer versions of Windows -- 7 and above -- weren't included in the MS14-063 patch, so they dug around and discovered that the bug appears to have been silently fixed in the newer versions of Windows. The flaw could allow an attacker to insert a malicious USB into a machine to ultimately wrest control of it.

Marc Maiffret, CTO at BeyondTrust, says it's unclear if the relatively late patch for the older versions of the OS resulted from an oversight by Microsoft or a "silent patch," where the software company made the fix in the newer OSes but for some reason didn't go back and do the same with the older versions of Windows.

"At some point, Windows 7 and newer versions were specifically fixed. The worry here when you have [only] some supported OSes getting fixed but not all, you wonder if the Cisco [researcher] was the first person to come across this or it had been used in attacks previously?" says Maiffret, whose firm posted a blog today on its findings.

"Years later now, we're lucky they found it," Maiffret says. "This is a great example of how you're really left a bit more insecure by running older, major OS versions -- even [vendor] supported ones."

Microsoft declined to comment for this article.

USB-born attacks got major exposure after the discovery of Stuxnet, which featured a poisoned USB attack at Iran's Natanz uranium enrichment facility. Most recently, researchers at Black Hat USA revealed the so-called BadUSB attack, where they reverse engineered and reprogrammed USB firmware to serve as a malware weapon. "The idea of USB memory sticks being attack vectors continues to grow," Maiffret says.

According to BeyondTrust: "This means that for many years now a vulnerability has existed in Windows 2003, 2008, Vista and XP systems while Windows 7 and above systems were fixed either accidentally or by a developer not taking the time to backport this fix into older, but still supported, operating systems."