The Remote Desktop Protocol (RDP) implementation in Microsoft Windows 7 SP1, Windows 8, Windows 8.1, and Windows Server 2012 Gold and R2 does not properly encrypt sessions, which makes it easier for man-in-the-middle attackers to obtain sensitive information by sniffing the network or modify session content by sending crafted RDP packets, aka "RDP MAC Vulnerability."
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2014/ms14-030
http://www.securityfocus.com/bid/67865