If exploited, attackers can gain full access to SharePoint content and potentially pivot to Outlook, Teams, and OneDrive. Learn how to protect your SharePoint server from compromise.

The term "zero-day" attack refers to when a previously unknown vulnerability is targeted. Tens of thousands of servers are said to be at risk. While the issue is serious, it differs from several previous vulnerabilities related to Microsoft. The attack only affects on-premises servers; cloud-based servers are unaffected.

Microsoft released a patch Monday for SharePoint Server 2016 that protects customers against a pair of vulnerabilities, which have been widely exploited in a wave of cyberattacks known as “ToolShell.”