Microsoft Exchange Server is prone to an information-disclosure vulnerability. Attackers can exploit this issue to obtain sensitive information that may aid in launching further attacks.
Block external access at the network boundary, unless external parties require service.
If global access isn't needed, block access at the network perimeter to computers hosting the vulnerable operating system.
Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy NIDS to monitor network traffic for signs of anomalous or suspicious activity such as unexplained incoming and outgoing traffic. This may indicate exploit attempts or activity that results from successful exploits.
Communicate sensitive information through secure means.
Implement multiple layers of encryption and authentication to help mitigate against exposure from this and other latent vulnerabilities.
Updates are available. Please see the references or vendor advisory for more information.