Microsoft Exchange Server Elevation of Privilege Vulnerability

An elevation of privilege vulnerability exists in Microsoft Exchange Server. An attacker who successfully exploited this vulnerability could gain the same rights as any other user of the Exchange server. This could allow the attacker to perform activities such as accessing the mailboxes of other users.

Exploitation of this vulnerability requires Exchange Web Services (EWS) and Push Notifications to be enabled and in use in an affected environment. To exploit the vulnerability, an attacker would need to execute a man-in-the-middle attack to forward an authentication request to a Microsoft Exchange Server, thereby allowing impersonation of another Exchange user.

To address this vulnerability, Microsoft has changed the notifications contract established between EWS clients and Exchange Servers to not allow authenticated notifications to be streamed by the server. Instead, these notifications will be streamed using anonymous authentication mechanisms.