Microsoft has released Security Updates (SUs) for vulnerabilities found in:
- Exchange Server Subscription Edition (SE)
- Exchange Server 2019
- Exchange Server 2016
SUs are available for the following specific versions of Exchange Server:
The October 2025 SUs address vulnerabilities responsibly reported to Microsoft by security partners and found through Microsoft’s internal processes. Although we are not aware of any active exploits in the wild, our recommendation is to immediately install these updates to protect your environment.
These vulnerabilities affect Exchange Server. Exchange Online customers are already protected from the vulnerabilities addressed by these SUs and do not need to take any action other than updating any Exchange servers or Exchange Management tools workstations in their environment.
More details about specific CVEs can be found in the Security Update Guide (filter on Server Software under Product Family).
Last publicly released updates for Exchange 2016 and 2019
October 2025 SUs are the last publicly available SUs for Exchange Server 2016 and 2019. From this point forward, only customers who contacted their Microsoft Account Teams to get the Extended Security Update (ESU) for those versions will receive new SUs that we might release for Exchange 2016 and 2019, through April 2026.
Our recommendation is that you upgrade your organization to Exchange SE rather than get the Exchange 2016 and 2019 ESU. Please remember that starting with Exchange SE CU2, there will be no more coexistence with Exchange 2016 and 2019 (CU2 will block installation if any build of Exchange 2016 or 2019 are present in the organization).
Auth Certificate export no longer possible via Export-ExchangeCertificate
Starting October 2025 SU, exporting the Exchange Server Auth Certificate and its private key with Export-ExchangeCertificate will be blocked for added security (see KB5069337 for details). The Auth Certificate is crucial for securing Exchange Server workloads, and exporting its private key is rarely needed. For Auth Certificate issues, use the MonitorExchangeAuthCertificate PowerShell script to assist with troubleshooting.
Update installation
The following update paths are available:
- Inventory your Exchange Servers to determine which updates are needed using the Exchange Server Health Checker script. Running this script will tell you if any of your Exchange Servers are behind on updates (CUs, SUs, or manual actions).
- Install the latest CU. Use the Exchange Update Wizard to choose your current CU and your target CU to get directions.
- Re-run the Health Checker after you install an update to see if any further actions are needed.
- If you encounter errors during or after installation of Exchange Server, run the SetupAssist script. If something does not work properly after updates, see Repair failed installations of Exchange Cumulative and Security updates. Also please see File version error when you try to install Exchange Server updates.
FAQs
Our organization is in Hybrid mode with Exchange Online. Do we need to do anything?
Exchange Online is already protected, but this SU needs to be installed on your Exchange servers, even if they are used only for management purposes. If you change the auth certificate after installing an SU, you should re-run the Hybrid Configuration Wizard.
The last SU/HU we installed is a few months old. Do we need to install all SUs in order to install the latest one?
SUs are cumulative. If you are running a CU supported by the SU, you do not need to install all SUs or HUs in sequential order; simply install the latest SU. Please see this blog post for more information.
Do we need to install SUs on all Exchange Servers within our organization? What about ‘Management Tools only’ machines?
Our recommendation is to install SUs on all Exchange Servers and all servers and workstations running the Exchange Management Tools to ensure compatibility between management tools clients and servers. If you are trying to update the Exchange Management Tools in the environment with no running Exchange servers, please see this.
Documentation may not be fully available at the time this post is published.
This post might receive future updates; they will be listed here (if available).
The Exchange Server Team
