Multiple serious vulnerabilities have been found in Microsoft Exchange Server. Malicious users can exploit these vulnerabilities to cause denial of service or obtain sensitive data.

These vulnerabilities are related to Oracle Outside In libraries elements and can be exploited by unauthenticated attacker with network access via HTTP.

Microsoft Exchange Server 2010 Service Pack 3
Microsoft Exchange Server 2013
Microsoft Exchange Server 2016

Install necessary updates from the KB section, that are listed in your Windows Update (Windows Update usually can be accessed from the Control Panel)

4099852
4295699
4099855