Microsoft has released security updates for vulnerabilities found in:
All versions (Cumulative Update levels) are impacted. Updates are available for the following specific builds of Exchange Server:
IMPORTANT: If manually installing security updates, you must install .msp from elevated command prompt (see Known Issues in update KB article).
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).
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
Nothing; schema was extended during installation of June 2021 CUs.
Exchange 2016 CU20 or
Extend the schema using June 2021 CUs.
Exchange 2013 CU23
- 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.
Older versions of Exchange (earlier than 2013)
Exchange no longer installed in the forest
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:
System.NullReferenceException: Object reference not set to an instance of an object. Please see this KB article for resolution.
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:
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).
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 installation, see the SetupAssist script. If something does not work properly after updates, see Repair failed installations of Exchange Cumulative and Security 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.
Updates to this post:
The Exchange Team
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