Technical Information

Brief overview of the risk:
This security update resolves two privately reported vulnerabilities and one publicly disclosed vulnerability in Microsoft Server Message Block (SMB) Protocol. The vulnerabilities could allow remote code execution on affected systems.
Detailed Information on the risk:

An unauthenticated remote code execution vulnerability exists in the way that Microsoft Server Message Block (SMB) Protocol software handles specially crafted SMB packets. An attempt to exploit the vulnerability would not require authentication, allowing an attacker to exploit the vulnerability by sending a specially crafted network message to a computer running the Server service. An attacker who successfully exploited this vulnerability could take complete control of the system. Most attempts to exploit this vulnerability would result in a system denial of service condition, however remote code execution is theoretically possible.

Further information on this exploit is available at : MS09-001