Microsoft Releases Emergency Patches for Actively Exploited SharePoint Zero-Days

Microsoft has released emergency security updates for two actively exploited zero-day vulnerabilities in SharePoint, tracked as CVE-2025-53770 and CVE-2025-53771, that have compromised servers worldwide in what researchers call "ToolShell" attacks. The U.S. Cybersecurity and Infrastructure Security Agency warned over the weekend that hackers were exploiting the vulnerabilities to gain remote code execution on on-premises SharePoint installations, while Microsoft has not yet provided patches for all affected versions.

The vulnerabilities allow hackers to steal private digital keys from SharePoint servers without requiring credentials, enabling them to plant malware and access stored files and data. Eye Security, which first identified the attacks on Saturday, found dozens of actively exploited servers and warned that SharePoint's integration with Outlook, Teams, and OneDrive could enable further network compromise. Researcher Silas Cutler at cybersecurity firm Censys estimated more than 10,000 companies with SharePoint servers were at risk, with the largest concentrations in the United States, Netherlands, United Kingdom, and Canada.

Microsoft released patches for SharePoint 2019 and Subscription Edition but is still working on fixes for SharePoint Server 2016. Administrators must install available updates immediately and rotate machine keys to prevent re-compromise, according to Microsoft's security guidance.

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