Microsoft CVE-2018-0924: Microsoft Exchange Information Disclosure Vulnerability

An information disclosure vulnerability exists in the way that Microsoft Exchange Server handles URL redirects. If an impacted user is using Microsoft Exchange Outlook Web Access (OWA) Light, the vulnerability could allow an attacker to discover sensitive information that should otherwise not be disclosed, such as the URL of the user's OWA service.
To exploit the vulnerability, an attacker could embed a link in an email and send it to a victim. The attacker would then have to trick the user into clicking the link. The attacker would be unable to force the user to click the link.
The security update addresses the vulnerability by correcting how Microsoft Exchange handles URL redirects.