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Microsoft released several Security Updates (SUs) for Microsoft Exchange Server to address vulnerabilities that have been used in limited targeted attacks. Due to the critical nature of these vulnerabilities, we recommend that customers apply the updates to affected systems immediately to protect against these exploits and to prevent future abuse across the ecosystem.
Note: These vulnerabilities affect Microsoft Exchange Server. Exchange Online is not affected.
Exchange Server Security Updates
Microsoft has released a set of out of band Security Updates for vulnerabilities for the following versions of Exchange Server:
- Exchange Server 2013
- Exchange Server 2016
- Exchange Server 2019
Security Updates are available for the following specific versions of Exchange:
- Exchange Server 2010 (for Service Pack 3 – this is a Defense in Depth update)
- Exchange Server 2013 (CU23)
- Exchange Server 2016 (CU18, CU19)
- Exchange Server 2019 (CU7, CU8)
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.
These vulnerabilities are used as part of an attack chain. The initial attack requires the ability to make an untrusted connection to Exchange server port 443. This can be protected against by restricting untrusted connections, or by setting up a VPN to separate the Exchange server from external access. Using this mitigation will only protect against the initial portion of the attack; other portions of the chain can be triggered if an attacker already has access or can convince an administrator to run a malicious file.
Because we are aware of active exploits of related vulnerabilities in the wild (limited targeted attacks), our recommendation is to install these updates immediately to protect against these 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 March 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.