The flaw, in the Microsoft Server Message Block (SMB) Protocol, could cause a system to stop functioning or become unreliable. Microsoft has issued a security advisory to confirm the issue and offer pre-patch mitigations. There is no risk of code execution that would allow an attacker to take control of, or install malware on, the company said. Default firewall settings on Windows 7 will help block attempts to exploit this vulnerability. Blocking TCP ports 139 and 445 at the firewall will help protect systems that are vulnerable.
Source: https://threatpost.com/ms-confirms-windows-7-dos-flaw-111609/73104/