Active Exploitation of Microsoft SharePoint Flaw CVE-2026-45659 Confirmed

The US Cybersecurity and Infrastructure Security Agency (CISA) has added CVE-2026-45659, a remote code execution vulnerability in Microsoft SharePoint, to its Known Exploited Vulnerabilities catalog due to active exploitation. This flaw, stemming from an untrusted data deserialization issue, affects SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Enterprise Server 2016. Microsoft released a patch for this vulnerability on May 21, 2026, but details were inadvertently omitted from the update bulletin. Organizations using SharePoint are urged to verify their patch levels and implement incident response procedures if they have not updated. The vulnerability allows authenticated attackers with minimal privileges to exploit it, potentially granting access to sensitive resources. CISA has mandated that federal agencies patch this vulnerability by July 4, 2026, emphasizing the urgency of remediation for all exposed organizations. No specific incidents of exploitation have been reported yet.

Key Points: • CVE-2026-45659 is a critical RCE vulnerability in Microsoft SharePoint with active exploitation. • Microsoft's patch for this flaw was released on May 21, 2026, but details were omitted. • CISA requires federal agencies to patch this vulnerability by July 4, 2026, highlighting its urgency.