CVE-2026-58644: Microsoft SharePoint Server Unauthenticated Remote Code Execution Vulnerability Exploited in the Wild

Overview On July 14, 2026, Microsoft published a security advisory addressing CVE-2026-58644 , a critical remote code execution (RCE) vulnerability affecting on-premises Microsoft SharePoint Server deployments. The vulnerability, which carries a CVSS v3.1 score of 9.8 (Critical), results from the deserialization of untrusted data ( CWE-502 ) and allows an unauthenticated attacker to execute arbitrary code. Microsoft confirmed active exploitation of CVE-2026-58644, and the vulnerability was subsequently added to CISA’s Known Exploited Vulnerabilities ( KEV ) catalog on July 16, 2026.