Microsoft is enhancing the security of the Windows kernel by eliminating trust for kernel drivers not certified through the Windows Hardware Compatibility Program (WHCP) starting with the April 2026 Windows Update. This change specifically targets kernel drivers signed by the now-obsolete cross-signed root program, which has been associated with security vulnerabilities. The new policy will initially be introduced in an "evaluation mode" to monitor and audit driver loads for potential compatibility issues. Custom kernel drivers can still be used under the Application Control for Business policy, but must be signed by an authority within the device's Secure Boot Platform Key or Key Exchange Key variables. The changes will impact Windows 11 versions 24H2, 25H2, 26H1, and Windows Server 2025.