Today we are announcing the availability of quarterly servicing updates, cumulative and update rollups, for all supported versions of Exchange Server. Exchange Server 2010, 2013, 2016 and 2019 all receive an update package. These updates include important fixes to address vulnerabilities being discussed in blogs and other social media outlets. While it is not the normal or preferred practice to release security updates in a cumulative update package, the nature of the product changes dictate that they be delivered this way as they include changes to the setup and configuration of Exchange Server. Additional details and recommended customer actions follow.
Changes to Exchange Web Services Push Notifications
An architectural change to Exchange Web Services (EWS) Push Notifications authentication is included in all packages released today. KB4490060 outlines the details of the changes made. Customers who rely upon Push Notifications, should understand the important changes made. We have evaluated the changes to push notifications against many commonly used EWS clients, e.g. Outlook Mac, Skype for Business Client, native iOS mail clients and observed no loss of functionality due to these changes. EWS Pull and Streaming Notifications functionality are unchanged by today’s updates.
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.
After applying either the cumulative update or update rollup to a server, customers are advised to force a reset of the Exchange servers’ credentials stored in Active Directory. This can be accomplished using the Reset-ComputerMachinePassword cmdlet in PowerShell 5.1 or later. If PowerShell is not an option, netdom can also be used. Microsoft knows of no instances where machine accounts have been compromised. Updating a machine account password is considered a best practice to ensure the security of the server is not compromised. In addition, customers are encouraged to evaluate if their user password expiration policies are appropriate for Exchange enabled accounts.
Decreasing Exchange Rights in the Active Directory
The Exchange team has determined a change in the Active Directory rights granted to Exchange Servers using the default Shared Permissions Model is in order. Changes in the latest cumulative updates, described in KB4490059, reduce the scope of objects where Exchange is able to write security descriptors in the directory.
In order to apply these changes, a directory admin will need to run the cumulative update setup program with the /PrepareAD parameter. When multiple Exchange versions co-exist in a single Active Directory forest, the cumulative update matching the latest version of Exchange deployed should be used to run /PrepareAD. Setup will automatically run /PrepareDomain in the domain where /PrepareAD is executed. Environments with multiple domains in the forest will need to run the cumulative update setup program using the /PrepareDomain parameter in all domains in the forest. These steps will update the rights granted to Exchange Servers in the Active Directory to meet the new permissions scope. More information on /PrepareAD and /PrepareDomain is available at this link.
Customers running only Exchange Server 2010 will need to follow the instructions in KB4490059 to update their environments. The update rollup package released for 2010 will not apply the directory changes.
The directory updates described in KB4490059 are fully compatible with all versions of Exchange Server regardless of cumulative update or update rollup version deployed. There is no loss of product functionality associated with these updates.
The rights granted to Exchange in Active Directory using the Active Directory Split Permissions Model are unchanged by the updates released today.
Shared Permissions vs. Split Permissions Model
Early advisories released by Microsoft related to this vulnerability indicated that Active Directory Split Permissions Model was a possible mitigation to Domain Admin elevation. It is true Split Permissions affords additional directory protection over the Shared Permissions Model. However, Microsoft fully supports both modes of directory operation and recognizes that there are relative strengths and weaknesses inherent to both models. Before implementing a change of this type, customers should fully evaluate the impact to line of business processes, security and operational needs. The changes released today improve the security profile of the Shared Permissions Model, while retaining the administrative flexibility it affords. The combination of the directory permission changes and EWS security change provides the best possible protection against possible attacks, meaning that Active Directory Split Permissions are not required, but still optional.
Removing Legacy Auth protocols from Exchange Servers
The Exchange team has been hard at work adding a feature to limit legacy authentication mechanisms on a user by user basis. In Exchange Server 2019 Cumulative Update 1, we are announcing new cmdlet support to create organization policies that restrict legacy authentication protocols. Policies can be defined which restrict legacy authentication on a per protocol and user by user basis. The capabilities added are based upon the same functionality already available in Office 365. In the days ahead, we will release additional details on this blog concerning this exciting new feature.
The KB articles that describe the fixes in each release and product downloads are available as follows:
- Exchange Server 2019 Cumulative Update 1 (KB4471391), VLSC Download
- Exchange Server 2016 Cumulative Update 12 (KB4471392), Download, UM Lang Packs
- Exchange Server 2013 Cumulative Update 22 (KB4345836), Download, UM Lang Packs
- Exchange Server 2010 Service Pack 3 Update Rollup 26 (KB4487052), Download, also available on Microsoft Update
Microsoft recommends all customers test the deployment of any update in their lab environment to determine the proper installation process for your production environment. For information on extending the schema and configuring Active Directory, please review the appropriate Microsoft Docs documentation.
Also, to prevent installation issues you should ensure that the Windows PowerShell Script Execution Policy is set to “Unrestricted” on the server being upgraded or installed. To verify the policy settings, run the Get-ExecutionPolicy cmdlet from PowerShell on the machine being upgraded. If the policies are NOT set to Unrestricted you should use the resolution steps in KB981474 to adjust the settings.
Reminder: Customers in hybrid deployments where Exchange is deployed on-premises and in the cloud, or who are using Exchange Online Archiving (EOA) with their on-premises Exchange deployment are required to deploy the currently supported cumulative update for the product version in use, e.g., 2013 Cumulative Update 22, 2016 Cumulative Update 12 or 11.
For the latest information on Exchange Server and product announcements please see What's New in Exchange Server 2016 and Exchange Server 2016 Release Notes. You can also find updated information on Exchange Server 2013 in What’s New in Exchange Server 2013, Release Notes and product documentation available on Microsoft Docs.
The updates released today will replace the quarterly servicing updates originally planned for March. The next planned set of quarterly updates is targeted for delivery in June.
Important: To avoid a setup failure, it is necessary to install the Visual C++ 2012 runtime before installing Cumulative Update 22 or Cumulative Update 12 on Edge role if not already present.
Note: Documentation may not be fully available at the time this post is published.