We are contacting you to alert you to Microsoft’s release of security updates for multiple different on-premises Microsoft Exchange Server zero-day vulnerabilities that are being exploited by a nation-state affiliated group.
The vulnerabilities exist in on-premises Exchange Servers 2013, 2016, and 2019. Exchange Online is not affected.
I want to ensure you are aware of the situation and urge you help drive immediate remediation steps:
• Microsoft highly recommends that you take immediate action to apply the patches for any on-premises Exchange deployments you have at your business, are hosting and managing for a customer.
• The first priority are servers that are accessible from the Internet (e.g., servers publishing Outlook on the web/OWA and ECP).
• To patch vulnerabilities, you should move to the latest Exchange Cumulative Updates and then install the relevant security updates on each Exchange Server.
• You can use the Exchange Server Health Checker script, which can be downloaded from GitHub (use the latest release).
• Running this script will tell you if you are behind on your on-premises Exchange Server updates (note that the script does not support Exchange Server 2010).
• We also recommend that your security team assess whether or not the vulnerabilities are being exploited by using the Indicators of Compromise we shared here. Optimus is available to assist in working on this with you.
• Please see the list of resources below for more information. We are committed to working with you through this issue.
• Microsoft On the Issues blog
Exchange patch information
• March 2, 2021 Security Update Release – Release Notes – Security Update Guide – Microsoft