November 2023 Exchange Server Security Updates

Microsoft released several Security Updates (SUs) for Microsoft Exchange Server to address vulnerabilities. Due to the critical nature of these vulnerabilities, we recommend that customers apply the November 2023 Exchange Server Security Updates to affected systems immediately to protect the environment.

Note: These vulnerabilities affect Microsoft Exchange Server. Exchange Online is not affected.

Exchange Server Security Updates

Microsoft has released Security Updates for vulnerabilities found in:

• Exchange Server 2016
• Exchange Server 2019

These Security Updates are available for the following specific versions of Exchange:

• Exchange Server 2016 (CU23)
• Exchange Server 2019 (CU12, CU13)

Read more on how to Install Exchange Security Update.

If you are not at these Exchange Server CU versions, please update right now and apply the above patch.

Read more on how to Install Exchange Cumulative Update.

Certificate signing of PowerShell serialization payload is now enabled by default

Certificate-based signing of PowerShell serialization payloads was introduced in the January 2023 Exchange Server Security Update. By default, the feature was released as disabled (opt-in) and had to be enabled by the Exchange Server administrator.

By installing the November 2023 (or later version) Exchange Server Security Update, the feature is enabled by default (opt-out) on a per-server basis, and has to be disabled if you don’t want to use it.

Note: Disabling certificate signing of PowerShell serialization payloads makes your server vulnerable to known Exchange Server vulnerabilities and weakens protection against unknown threats. We recommend that you leave this feature enabled.

Known issues in this update

• There are no known issues with this update

Issues that are fixed in this update

The following issues have been resolved in this update:

• Signing of the serialisation payload fails to run the few cmdlets
• Unable to migrate mailbox as communication error parameter exception occurs

FAQs

How does this SU relate to Extended Protection feature?
If you already enabled Extended Protection on your servers, install the SU as usual. If you did not enable Extended Protection yet, our recommendation is to enable it after installing January (or any later) SU. Running Health Checker script will always help you validate exactly what you might need to do after SU installation.

Is Windows Extended Protection a prerequisite that needs to be activated before or after applying the SU, or is that an optional but strongly recommended activity?
Extended Protection is not a prerequisite for this Security Update. You can install it without having to activate the Extended Protection feature. However, configuring Extended Protection is strongly recommended, which can help you protect your environments from authentication relay or “Man in the Middle” (MITM) attacks.

The last SU that we installed is (a few months old). Do we need to install all SUs in order, to install the latest one?
The Exchange Server Security Updates are cumulative. If you are running the CU that the SU can be installed on, you do not need to install all the SUs in sequential order but can install the latest SU only.

My organization is in Hybrid mode with Exchange Online. Do I need to do anything?
While Exchange Online customers are already protected, the November 2023 Security Update needs to be installed on your on-premises Exchange Servers, even if they are used only for management purposes. You do not need to re-run the Hybrid Configuration Wizard (HCW) after applying updates.

Do I need to install the updates on “Exchange Management Tools only” workstations?
Install Security Updates on all Exchange Servers as well as servers or workstations running Exchange Management Tools only, which will ensure that there is no incompatibility between management tools clients and servers.

Further information

• Exchange Team Blog
• CVE-2023-36035
• CVE-2023-36039
• CVE-2023-36050
• CVE-2023-36439