Microsoft said it is investigating the flaw, but provided no information on any analysis it's conducted thus far.

"Microsoft is investigating public claims of a possible vulnerability in Windows SMB [Server Message Block]," said Jerry Bryant, a group manager with the Microsoft Security Response Center (MSRC), in an e-mail Tuesday. "Once we're done investigating, we will take appropriate action to help protect customers. This may include providing a security update through the monthly release process, an out-of-cycle update or additional guidance to help customers protect themselves."

The researcher, identified only as "Cupidon-3005," posted exploit code Monday for the vulnerability, which is reportedly in the "BowserWriteErrorLogEntry()" function within the "mrxsmb.sys" driver. The driver processes requests to the Server Message Block protocol that Windows uses for network communication.

SMB is mainly used to provide file- and printer-sharing to Windows machines.

According to French security company Vupen, which rated the bug as a successful exploit could "cause a denial of service or take complete control of a vulnerable system." The former would crash Windows and produce the notorious "Blue Screen of Death" that illustrates a serious collapse of the operating system.