Microsoft Exchange is prone to a remote denial-of-service vulnerability because it fails to properly handle specially crafted IMAP commands. Successfully exploiting this issue allows remote attackers to cause targeted Exchange servers' mail service to stop responding, thus denying further email service for legitimate users. To recover from the denial-of-service condition, administrators must restart the IIS Admin Service service.
Block external access at the network boundary, unless external parties require service.
Ensure that only trusted hosts and networks can connect to vulnerable servers.
Disallow anonymous access to services. Permit access for trusted individuals only.
Disable unauthenticated access to servers to limit the potential for anonymous remote attackers to exploit this issue.
Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy NIDS to detect and block attacks and anomalous activity such as requests containing suspicious IMAP commands. Since the application may log such requests, review its logs regularly.
The vendor has released an advisory along with updates to address this issue. Please see the referenced advisory for more information.