SharePoint Server 2019

Critical Microsoft SharePoint Vulnerability Allows Remote Code Execution via SafeControls Bypass

A vulnerability tracked as CVE-2026-65660 with a CVSS score of 8.8 affects Microsoft SharePoint Server 2016, SharePoint Server 2019, and Subscription Edition. The flaw permits an authenticated low-privileged attacker to achieve arbitrary code execution on on-premises servers. It stems from improper handling of quotes in attacker-controlled Register directives within the ToolPane component, bypassing the SafeControls mechanism. This allows registration of dangerous .NET classes followed by deserialization-based remote code execution. Microsoft released patches on August 11, 2026, and initially reported no public disclosure or exploitation. Publication of a detailed technical analysis has now increased the risk for unpatched installations.

Attackers Actively Exploit Critical SharePoint Authentication Bypass CVE-2026-55040 After Public PoC Release

Active exploitation of CVE-2026-55040, a critical authentication bypass vulnerability in Microsoft SharePoint Server, has intensified following the public release of a proof-of-concept exploit. The flaw, which carries a CVSS score of 9.1, stems from multiple defects in the JWT token validation pipeline and allows remote attackers to impersonate any user, including administrators, without valid credentials. Affected versions include SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Server 2016, with heightened risk for instances exposed to the internet. Microsoft released patches in July 2026, and organizations are urged to apply them immediately while restricting external access and monitoring IIS logs for anomalous administrative activity. The vulnerability has already been chained with other flaws in real-world incidents involving persistence, data theft, and credential rotation responses.