Recommended audience for this post: Exchange Administrators, System Administrators, IT Managers, and CIOs.


On 13 April 2021, Microsoft released security updates to mitigate significant newly discovered vulnerabilities in Microsoft Exchange 2013, 2016 and 2019. These vulnerabilities could be exploited by attackers to gain and persist access to Microsoft Exchange deployments. The patches previously released by Microsoft in March 2021 do not remediate these new vulnerabilities and organisations must apply Microsoft’s 13 April 2021 updates to prevent potential compromise.

The new vulnerabilities are:

How can I check if my Microsoft Exchange Server has been compromised?

Currently, there are no indicators or tests to determine a breach, and we are not aware of any active exploits in the wild. However, we recommend all Microsoft Exchange Server 2013/2016//2019 customers install Microsoft’s updates immediately to protect their environment.

What can I do NOW to protect my Exchange environment from the exploit?

  • SLA Clients of AVeS Cyber Security: The A-Team would have installed the KB5001779 update to protect your Exchange environment. You can get a report of Exchange Server Version and Update statistics to verify that the update has been done.
  • Non-SLA Clients: Check the current Exchange Server Version and Update statistics. Install KB5001779 to protect the Exchange environment, or contact us to assist you.

What else can I do to protect my Exchange environment in the future?

  1. Install all the latest security updates from Microsoft to all Windows servers.
  2. Ensure that regular patch cycles run successfully. Assess and remediate any issues that would prevent regular updates from being deployed.
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