Microsoft’s Threat Intelligence team, leveraging the capabilities of its Security Copilot AI tool, has identified critical vulnerabilities in widely-used open-source bootloaders, including GRUB2, U-Boot, and Barebox.
These vulnerabilities pose significant risks to systems utilizing Unified Extensible Firmware Interface (UEFI) Secure Boot and embedded devices.
The findings highlight the potential for attackers to execute arbitrary code, bypass Secure Boot protections, and install stealthy bootkits.
Streamlining Vulnerability Analysis with AI
Microsoft Security Copilot significantly accelerated the vulnerability discovery process by focusing on high-risk areas such as filesystem handling within bootloader code.
Through iterative prompts and automated analysis, the tool identified an exploitable integer overflow vulnerability in GRUB2’s filesystem implementation.
This discovery prompted further investigation into similar patterns across other components of GRUB2 and related bootloaders like U-Boot and Barebox, which share codebases with GRUB2.
The vulnerabilities uncovered include buffer overflows in symbolic link handling, file reads, and directory table parsing across various filesystems such as JFS, SquashFS, and EXT4.
Additionally, a cryptographic side-channel attack was identified in GRUB2 due to non-constant time memory comparisons.
These flaws expose systems to risks such as unauthorized code execution during the boot process and potential bypassing of security mechanisms like BitLocker.
Impact on Secure Boot and Embedded Systems
The implications of these vulnerabilities are severe. Exploiting flaws in GRUB2 could allow attackers to bypass UEFI Secure Boot a critical security protocol and gain full control over a device’s boot process.
This could lead to the installation of persistent malware or bootkits that remain active even after operating system reinstalls or hardware replacements.
In contrast, exploiting vulnerabilities in U-Boot and Barebox typically requires physical access to the device but still poses significant threats to embedded systems.
The vulnerabilities’ reach is amplified by the widespread practice of code reuse among open-source projects.
For instance, shared filesystem parsing code between GRUB2, U-Boot, and Barebox contributed to similar flaws across these platforms.
According to the Report, Microsoft disclosed these vulnerabilities to the respective maintainers of GRUB2, U-Boot, and Barebox.
Prompt action was taken: GRUB2 maintainers released patches on February 18, 2025, followed by updates for U-Boot and Barebox on February 19, 2025.
Fixes included addressing integer overflows, enhancing Secure Boot revocation management through SBAT updates, and disabling certain OS modules when Secure Boot is enabled to reduce attack surfaces.
The collaboration extended beyond maintainers to include manufacturers and the open-source community. Microsoft also credited Red Hat for assisting in responsible disclosure efforts.
This research underscores the transformative role of AI tools like Security Copilot in cybersecurity workflows.
By automating vulnerability identification and analysis tasks, Security Copilot saved researchers approximately a week’s worth of manual effort while ensuring comprehensive coverage of potential issues.
The findings not only enhance Microsoft’s security solutions but also contribute to broader industry efforts to secure devices across platforms.
As open-source software continues to underpin critical infrastructure globally, this incident highlights the importance of responsible disclosure practices and collaborative threat intelligence sharing to mitigate risks effectively.
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