The February 2019 Exchange Quarterly updates (https://blogs.technet.microsoft.com/exchange/2019/02/12/released-february-2019-quarterly-exchange-updates/) from Microsoft includes a fix for the NTLM relay vulnerability we reported last week. The fix changes the way Exchange Web Services operates in order to remove the ability for a man in the middle attack to capture and replay the authentication traffic and so escalate their privileges to the same rights as any other user of the Exchange server.
The update to EWS Push Notifications is considered a critical security update and customers should deploy the update as soon as they understand and accept any potential impact. The change in Push Notification authentication is a permanent change to the product and necessary to protect the security of an Exchange Server.
Details of the patch and how to install it are published by Microsoft here: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-0686