Urgent: On-Prem SharePoint Vulnerability CVE‑2025‑53770 (ToolShell) – What You Need to Know
Summary Microsoft has confirmed active exploitation of a critical on-premises SharePoint vulnerability, CVE‑2025‑53770-a variant of the previously identified CVE‑2025‑49706. This vulnerability allows unauthenticated remote code execution (RCE) on SharePoint servers. While SharePoint Online (Microsoft 365) is not affected, organizations using SharePoint Server 2016, 2019, and Subscription Edition are at immediate risk. At the time of this post, no official patch is available. Microsoft has issued interim mitigation guidance. What You Need to Know The vulnerability has been assigned a CVSS score of 9.8 (Critical). Exploits are being observed in the wild. Victims include public sector, education, and private industry servers globally. The exploit method, named "ToolShell" by researchers, involves a chain of vulnerabilities that allow attackers to gain full control of servers without authentication. Attackers exploit public-facing SharePoint servers using crafted requests that trigger deserialization flaws, ultimately installing web shells such as spinstall0.aspx to maintain persistent access. Microsoft's Guidance Microsoft…