Early last week, multiple so-called zero-day attacks, or attacks whose vulnerabilities are unknown to users, administrators and even vendors, impacted Microsoft Exchange servers. While unconnected at this point to the Orion SolarWinds supply-chain attack, the market penetration of Exchange makes it so that these zero-day vulnerabilities have the potential to be catastrophic for enterprise owners. These critical vulnerabilities impact on-premises servers that run Exchange Server 2013, Exchange Server 2016 and Exchange Server 2019, whereas Exchange Online products are currently unaffected.