Microsoft's UEFI bootloader signing key under Secure Boot, set to expire in September, could create issues for Linux users.
On September 11, 2025, a significant Microsoft signing key—used by many Linux distributions to support Secure Boot—is set to expire. This key is part of the Unified Extensible Firmware Interface (UEFI) and helps ensure booting with trusted software by the manufacturer.
What Happens When the Key Expires?
When the current Microsoft key expires, it will no longer be used to sign new versions of the Linux shim bootloader. Systems relying on this key for Secure Boot validation will stop accepting new, signed versions of the shim after this date. However, already signed binaries will remain valid if the system’s firmware does not enforce key expiry checks. The immediate impact: Linux distributions using the expiring key may not be able to boot securely on affected systems that only accept this key.
The New Key and Its Implementation
A replacement signing key has been available since 2023, but it may not be widely installed on existing hardware. For the new key to work, system firmware must include it in the database of trusted keys. This typically requires a firmware (UEFI/BIOS) update from the hardware manufacturer, but there is no guarantee all vendors will provide such updates, especially for older or less popular hardware.
Practical Consequences for Users
- Potential Boot Failures: If a system only trusts the expired key and receives a new, differently signed Linux bootloader, Secure Boot may fail, preventing Linux from booting unless Secure Boot is disabled.
- Reduced Security: Disabling Secure Boot to work around this issue removes a significant security feature, exposing users to bootkit and similar threats.
- OEM Coordination Required: The responsibility falls to hardware manufacturers to distribute firmware updates adding the new key. Users of systems not receiving such updates will face the greatest disruption.
- Windows Unaffected (For Now): This expiry does not immediately impact Windows systems, as they use a separate, longer-lived set of certificates (expiry in June 2026). However, Windows users should still be aware of forthcoming key transitions.
Community and Vendor Responses
Linux distributions, firmware tooling projects, and the broader community are discussing and planning mitigations, but there is no universal, user-friendly solution for all affected systems. Users are advised to check with their hardware vendors for firmware updates and monitor distribution announcements for guidance.
A Summary of the Situation
| Scenario | Impact on Linux Secure Boot | |---------------------------------------------|--------------------------------------------| | Firmware updated with new key | No disruption; Secure Boot continues | | Firmware not updated, uses expired key only | Secure Boot may fail with new Linux boot | | Secure Boot disabled | Linux boots, but security is reduced |
In summary, the upcoming expiry of the Microsoft-signed Secure Boot key poses a significant challenge for Linux users on systems that do not receive a firmware update to install the new key. Failure to update may result in Secure Boot failures or require users to disable Secure Boot, potentially reducing system security.
Technology in data-and-cloud computing plays a crucial role in this scenario, as the expiration of the Microsoft key for Linux Secure Boot is primarily an issue within the realm of technology.
To mitigate potential boot failures, users and distribution developers would need to embrace and adopt advanced technological solutions, such as firmware updates or alternative boot methods, to ensure seamless functionality and maintain the security of their systems after the key expiration.
