Microsoft Exchange Server is prone to a security-bypass vulnerability. An attacker can exploit this issue to bypass the same-origin policy, obtain sensitive information and perform unauthorized actions. This could be used to steal sensitive information or launch other attacks.
Block external access at the network boundary, unless external parties require service.
Filter access to the affected computer at the network boundary if global access isn't required. Restricting access to only trusted computers and networks might greatly reduce the likelihood of exploits.
Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy NIDS to monitor network traffic for anomalous or suspicious activity. Monitor logs generated by NIDS and by the server itself for evidence of attacks against the server.
Permit privileged access for trusted individuals only.
Permitting access to vulnerable applications for trusted individuals only can reduce the risk of an exploit.
Updates are available. Please see the references or vendor advisory for more information.