Microsoft has patched two critical holes this Patch Tuesday.
The more serious of the two flaws is a remote code execution vulnerability affecting Outlook and Exchange Server. It involves a format called Transport Neutral Encapsulation Format (TNEF), which is used when sending e-mail messages in Rich Text Format.
An attacker could gain administrative control of a compromised system, warned Microsoft.
What makes the TNEF flaw particularly dangerous is the fact that it exists in Exchange and Outlook - both widely used by companies - and does not require user participation.
"All that needs to take place is for an e-mail to get sent to a server," for the flaw to be exploited, said Michael Sutton, director at security expert iDefense. 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, said Alain Sergile, technical product manager at ISS' X-Force team. "We think that from a software engineering perspective, it will be fairly complicated to exploit, but it is feasible," he said.
The other flaw is in how 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.
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