Microsoft SharePoint Remote Code Execution (RCE) Vulnerability Advisory (CVE-2026-50522, CWE-502)

1. Apply Official Security Patches

Immediately install the official security updates provided by Microsoft.

• Refer to the Microsoft MSRC Update Guide for CVE-2026-50522 to download and apply the appropriate patch for your environment.

2. Temporary Mitigations (Prior to Patching)

If immediate patching is not feasible, implement the following workarounds:

• Network Access Control: Restrict external internet access to SharePoint web ports (typically TCP 80, 443, and administration ports). Limit access to trusted internal IP ranges or via VPN only.
• WAF (Web Application Firewall) Rules: Deploy and enable WAF signatures designed to detect and block suspicious serialized payloads (e.g., .NET BinaryFormatter or ObjectDataProvider patterns) in HTTP requests.

CVE-2026-50522 is a critical vulnerability arising from the deserialization of untrusted data (CWE-502) within Microsoft SharePoint Server.

An unauthenticated attacker can exploit this vulnerability by sending a specially crafted serialized payload to an exposed SharePoint endpoint. During the deserialization process on the server side, the malicious payload triggers arbitrary code execution under the security context of the SharePoint service account.

With a CVSS 3.1 score of 9.8 (Critical), this flaw requires no privileges (PR:N) and no user interaction (UI:N). Because this vulnerability is actively exploited in the wild and listed in the CISA KEV catalog, immediate remediation is highly recommended to prevent potential system compromise.