Source: https://msrc-blog.microsoft.com/blog/2021/03/guidance-for-responders-investigating-and-remediating-on-premises-exchange-server-vulnerabilities/
This guidance will help customers address threats taking advantage of the recently disclosed Microsoft Exchange Server on-premises vulnerabilities CVE-2021-26855, CVE-2021-26858, CVE-2021-26857, and CVE-2021-27065, which are being exploited. We strongly urge customers to immediately update systems. Failing to address these vulnerabilities can result in compromise of your on-premises Exchange Server and, potentially, other parts of your internal network.
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