"All that needs to take place is for an e-mail to get sent to a server" for the flaw to be exploited, Sutton said. This raises the possibility of widespread infections if an exploit ever becomes available for the flaw, he added.

But exploiting the flaw won't be particularly easy, Sergile said. "We think that from a software engineering perspective, it will be fairly complicated to exploit, but it is feasible," he said.

The other flaw disclosed Tuesday is also a privately reported vulnerability that exists in the way Windows handles malformed embedded Web fonts.

According to Microsoft's description, "An attacker could exploit the vulnerability by constructing a malicious embedded Web font that could potentially allow remote code execution if a user visited a malicious Web site or viewed a specially crafted e-mail message."

Though the flaw is also serious, it requires active user interaction for it to be exploited, thereby making it less dangerous than the TNEF flaw, Sutton said.