Introduction

After nearly nine months of challenges faced by Windows 11 users employing dual-boot configurations, Microsoft has released a fix addressing the critical issue that disrupted Linux booting on systems with Secure Boot enabled. This resolution comes after a prolonged period of user frustration and highlights the complexities involved in maintaining compatibility across diverse operating systems.

Background

In August 2024, Microsoft issued a security update aimed at mitigating vulnerabilities associated with the GRUB2 bootloader, specifically targeting the CVE-2022-2601 vulnerability. This update introduced Secure Boot Advanced Targeting (SBAT) settings designed to block unpatched or outdated boot managers. While intended to enhance system security, the update inadvertently affected dual-boot systems by preventing Linux distributions from booting, even when Secure Boot was enabled. Users encountered error messages such as:

CODEBLOCK0

This issue arose because the update's dual-boot detection mechanism failed to recognize certain customized dual-boot setups, leading to the unintended application of SBAT policies on systems that should have been exempt. (bleepingcomputer.com)

Microsoft's Response and Workarounds

Upon acknowledging the problem, Microsoft collaborated with Linux partners to investigate and address the issue. In the interim, the company provided a workaround for affected users, which involved:

  1. Disabling Secure Boot: Accessing the device's firmware settings to turn off Secure Boot.
  2. Deleting the SBAT Update: Booting into Linux and executing the command INLINECODE0 to remove the problematic SBAT policy.
  3. Re-enabling Secure Boot: Returning to the firmware settings to reactivate Secure Boot.
  4. Preventing Future SBAT Updates: In Windows, running a registry command to opt out of future SBAT updates.

These steps were detailed in Microsoft's official documentation and aimed to restore dual-boot functionality while maintaining system security. (bleepingcomputer.com)

Resolution and Implications

In May 2025, Microsoft released a comprehensive fix that addressed the dual-boot issue without requiring manual interventions from users. This update corrected the dual-boot detection mechanism, ensuring that SBAT policies were appropriately applied only to systems without dual-boot configurations.

The prolonged delay in resolving this issue underscores the challenges inherent in balancing security updates with system compatibility. For users who rely on dual-boot setups for development, testing, or personal preference, such disruptions can significantly impact productivity and workflow.

Technical Details

The root cause of the issue was the misapplication of SBAT policies due to inadequate detection of dual-boot configurations. SBAT is a mechanism within Secure Boot that allows for the revocation of vulnerable bootloaders by setting specific policy values. In this case, the update intended to block bootloaders susceptible to the CVE-2022-2601 vulnerability but inadvertently affected legitimate Linux bootloaders in dual-boot scenarios.

The final fix involved refining the detection algorithms to accurately identify dual-boot systems and applying SBAT policies selectively, thereby preserving the integrity and security of both Windows and Linux installations.

Conclusion

Microsoft's resolution of the Windows 11 dual-boot bug after a nine-month delay highlights the intricate balance between implementing security measures and maintaining system compatibility. This incident serves as a reminder of the importance of thorough testing and collaboration with the broader tech community to address issues that affect diverse user configurations.