Microsoft has issued a critical security update addressing CVE-2026-3783, a severe vulnerability affecting multiple Windows versions. Users must apply patches immediately to prevent potential exploitation.
Microsoft Releases Critical Security Update for CVE-2026-3783 Vulnerability
Microsoft has issued an emergency security update to address CVE-2026-3783, a critical vulnerability affecting Windows operating systems. The flaw, which carries a CVSS score of 9.8, allows remote code execution without authentication.
Vulnerability Details
The vulnerability exists in the Windows Remote Procedure Call (RPC) service, enabling attackers to execute arbitrary code on affected systems. Microsoft confirmed the issue impacts:
- Windows 10 versions 1809 through 22H2
- Windows 11 versions 21H2 through 23H2
- Windows Server 2019 and 2022
- Windows Server 2025 (all editions)
Successful exploitation requires no user interaction and can be triggered through network connections, making this vulnerability particularly dangerous for internet-facing systems.
Security Update Deployment
Microsoft has released the following security updates:
- KB5025239 for Windows 10 versions 1809-22H2
- KB5025240 for Windows 11 versions 21H2-23H2
- KB5025241 for Windows Server 2019/2022
- KB5025242 for Windows Server 2025
Updates are available through Windows Update, Microsoft Update Catalog, and WSUS. Microsoft strongly recommends immediate installation.
Mitigation Steps
Organizations unable to apply updates immediately should:
- Block TCP ports 135, 139, 445, and 49152-65535 at network boundaries
- Enable Windows Firewall with default settings
- Restrict RPC endpoint mapper access to trusted systems only
- Monitor for unusual RPC traffic patterns
Attack Timeline
Microsoft detected exploitation attempts beginning March 15, 2026, with initial reports from European financial institutions. The company coordinated with CISA and other agencies to develop and deploy the patch within 72 hours of discovery.
Additional Resources
Contact Information
Organizations requiring assistance should contact Microsoft Support or their managed service provider. Critical infrastructure operators should coordinate with CISA through the 24/7 Operations Center.
Microsoft will provide additional guidance through its monthly security update cycle on April 14, 2026.
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