This article describes the protection against the publicly disclosed Secure Boot security feature bypass that uses the BlackLotus UEFI bootkit tracked by CVE-2023-24932, how to enable the mitigations, and guidance on bootable media.

Fixes an issue in which a computer crashes in the BIOS on a Windows 8.1 or Windows Server 2012 R2-based computer.

Describes how to troubleshoot the error message "Bootmgr is missing Press Ctrl+Alt+Del to restart" that may occur when you try to start Windows.

Fixes a "Boot failed" error that occurs when you start a UEFI-enabled computer from a Windows 7 or Windows Server 2008 R2 installation DVD if a storage device has more than four partitions. Skip to main content

To run the Bootrec.exe tool, first start the Windows RE: Put the Windows Vista or Windows 7 media in the DVD drive, and then start the computer. Press a key when you are prompted. Select a language, a time, a currency, a keyboard, or an input method, and then click Next. Click Repair your computer.

This issue occurs because the boot manager compares two device signatures incorrectly. These device signatures are the Extensible Firmware Interface (EFI) device signature that is in the extended boot record (EBR) and the device signature that is in the master boot record (MBR).

Windows 7. The Advanced Boot Options screen lets you start Windows in advanced troubleshooting modes. You can access the menu by turning on your computer and pressing the F8 key before Windows starts. Some options, such as safe mode, start Windows in a limited state, where only the bare essentials are started.

To help keep Windows devices secure, Microsoft adds vulnerable bootloader modules to the Secure Boot DBX revocation list (maintained in the system UEFI-based firmware) to invalidate the vulnerable modules.

Symptoms. When trying to boot Windows, you receive the error: An operating system wasn’t found. Try disconnecting any drives that don’t contain an operating system. Press Ctrl+Alt+Del to restart. Resolution. A bootable USB or DVD with Windows 7 or higher is needed to bring up the Command Prompt.

This security update resolves a vulnerability in Microsoft Windows. The vulnerability could allow security feature bypass if an attacker installs an affected boot manager and bypasses Windows security features. To learn more about the vulnerability, see Microsoft Security Bulletin MS16-100.