The July 2021 security updates for Exchange Server address vulnerabilities responsibly reported 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 install these updates immediately to protect your environment.
These vulnerabilities affect on-premises Microsoft Exchange Server, including servers used by customers in Exchange Hybrid mode. Exchange Online customers are already protected and do not need to take any action.
More details about specific CVEs can be found in Security Update Guide (filter on Exchange Server under Product Family).
Latest /PrepareSchema needed for full effect
Because of additional security hardening work for CVE-2021-34470, the following actions should be taken in addition to application of July 2021 security updates:
The latest version of Exchange installed
Additional steps needed to extend AD schema
Exchange 2016 CU21 or Exchange 2019 CU10
Nothing; schema was extended during installation of June 2021 CUs.
- Install July 2021 Security Update for Exchange 2013
- Extend the Active Directory schema using the elevated Command prompt. Command will be similar to the following:
“Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms” using the setup.exe from location “c:\Program Files\Microsoft\Exchange Server\V15\Bin\setup.exe” (use the folder for the installation location of your Exchange server)
- For Exchange 2013 only, schema version will not change after this.
- In case of Schema Master existing in an empty root domain, consider installing Exchange CU23 Management Tools on Windows 2012 R2 in the same domain, installing July SU and then running \prepareschema from that workstation.
During the release of April 2021 SUs, we received some reports of issues after installation. The following issues reported for April 2021 SUs also apply to July SUs and have the following workarounds:
Administrator/Service accounts ending in ‘$’ cannot use the Exchange Management Shell or access ECP. The only workaround at this time is to rename Admin accounts or use accounts with no ‘$’ at the end of the name.
Some cross-forest Free/Busy relationships based on Availability address space can stop working (depending on how authentication was configured) with the error: “The remote server returned an error: (400) Bad Request.” Please see this KB article for how to solve this problem.
Cmdlets executed against the Exchange Management Console using an invoked runspace might fail with the following error message: The syntax is not supported by this runspace. This can occur if the runspace is in no-language mode. Please see this KB article for more information.
Installing June 2021 Cumulative Updates for Exchange 2016 or 2019 might fail with the error:
System.NullReferenceException: Object reference not set to an instance of an object. Please see this KB article for resolution.
Starting with July 2021 updates, users might be redirected back to the login page when using OWA/ECP if organization uses Load Balancing. You should avoid running mixed pools (servers with the latest SU applied together with servers which have not yet received the update). Please see this KB article for more information.
Prior to installing the Security Update (SU), we recommend you check if a valid Microsoft Exchange Server Auth Certificate is present on every Exchange server (except Edge Transport servers). The easiest way to do this is to run the Exchange Health Checker and check for the Auth Certificate output:
You can also run the following PowerShell command to check if the Auth Certificate is available on your system:
If there is no Auth Certificate or it has expired, then follow the steps outlined here to configure it correctly.
Please note: In some environments, it may take an hour for the OAuth certificate to be published. If you have a hybrid setup, you have to run the Hybrid Configuration Wizard again to update the changes to Azure Active Directory (Azure AD). If this certificate is missing or is expired, users may face issues logging in to OWA/ECP with HTTP 500 error after application of July updates. KB article is here.
Because of the recommended schema update requiring the latest set of June 2021 CUs, there are several scenarios that you might need to follow:
Inventory your Exchange Servers / determine which updates are needed
Use the Exchange Server Health Checker script (use the latest release) to inventory your servers. Running this script will tell you if any of your Exchange Servers are behind on updates (CUs and SUs).
Update to the latest Cumulative Update
Go to https://aka.ms/ExchangeUpdateWizard and choose your currently running CU and your target CU. Then click the “Tell me the steps” button, to get directions for your environment.
If you encounter errors during or after installation of Exchange Server updates
My organization is in Hybrid mode with Exchange Online. Do I need to do anything? While Exchange Online customers are already protected, the July 2021 security updates do need to be applied to 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? Servers or workstations running only Microsoft Exchange Management Tools (no Exchange services) do not need to apply these updates.
Instructions seem to indicate that for Exchange 2013, we should extend the schema after July 2021 SU is installed; is that correct? Yes. Because we did not release an Exchange 2013 Cumulative Update (CU) that contains the new schema updates, the July 2021 SU package updates the schema files in Exchange server folders when July 2021 SU is installed. That is why once those files are updated (SU is installed) – we ask you to go and explicitly update the schema using setup from \v15\Bin folder.
We have Exchange 2016 CU20 and 2019 CU9 servers and have installed July 2021 security updates but did not run /PrepareSchema using June 2021 CUs first. Is this a problem? No. Extension of AD schema using June 2021 CU is really a separate step that should be taken to address a specific CVE. There is no dependency in July 2021 SUs on this schema change, or vice versa. Just make sure that both of those actions are taken; order is not important.