A USB Mass Storage Class driver vulnerability that Microsoft fixed earlier this week may have been even more serious than the company originally described in its Patch Tuesday update, according to Kaspersky Lab's Threatpost blog.

The posted noted that Microsoft likely classified the flaw as “important,” and not “critical,” because at first glance it appears to require a hacker to locally access a vulnerable device and insert a malicious USB device into it in order to exploit it. However, research has shown that such bugs can sometimes be attacked remotely via Remote Desktop Protocol (RDP) and RemoteFX USB redirection features. In that case the threat would be seriously elevated.

Microsoft's Mar. 8 Security Bulletin said the flaw, MS16-033, constituted a failure on the part of the USB driver to “properly validate objects in memory. A successful attacker could run arbitrary code in kernel mode and could then install programs; view, change, or delete data; or create new accounts with full user rights.”