This article summarizes Microsoft’s release of patches 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 2010, 2013, 2016, and 2019. Exchange Online is not affected.
Specifically, to minimize or avoid impacts of this situation, Microsoft highly recommends that you take immediate action to apply the patches for any on-premises Exchange deployments. The first priority being servers which are accessible from the Internet (e.g., servers publishing Outlook on the web/OWA and ECP).
To patch these 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 were being exploited by using the Indicators of Compromise we shared here.
- Microsoft On the Issues blog
- Microsoft Security Response Center (MSRC) release - Multiple Security Updates Released for Exchange Server
- Exchange Team Blog
- MSTIC Blog
- MSRC Blog
- Microsoft On the Issues Blog
- Out of Band Exchange Release Customer Alert
- Security Update Guide
Exchange Patch Information
- March 2, 2021 Security Update Release – Release Notes – Security Update Guide – Microsoft
- CVE-2021-26855 | Microsoft Exchange Server Remote Code Execution Vulnerability (public)
- CVE-2021-26857 | Microsoft Exchange Server Remote Code Execution Vulnerability (public)
- CVE-2021-26858 | Microsoft Exchange Server Remote Code Execution Vulnerability (public)
- CVE-2021-27065 | Microsoft Exchange Server Remote Code Execution Vulnerability (public)