Microsoft Discovers Critical Vulnerabilities in GRUB2, U-Boot, and Barebox Bootloaders Using AI-Powered Copilot

Microsoft has identified multiple critical vulnerabilities in widely used bootloaders, including GRUB2, U-Boot, and Barebox. These security flaws expose systems to sophisticated boot-level attacks, potentially compromising devices before the operating system initializes. Attackers exploiting these vulnerabilities could achieve persistent and nearly undetectable control over affected systems.

These vulnerabilities impact thousands of Linux-based systems and embedded devices that rely on these open-source bootloaders for hardware initialization and OS loading. GRUB2 (Grand Unified Bootloader version 2) is particularly concerning due to its extensive use in enterprise Linux distributions and secure boot implementations. Similarly, vulnerabilities in U-Boot and Barebox pose significant risks to embedded systems, IoT devices, and network appliances, expanding the attack surface across multiple industries.

Microsoft researchers discovered these flaws during a proactive security review using their AI-powered Copilot tool to analyze bootloader codebases. Their investigation revealed that certain memory handling functions within these bootloaders fail to properly validate input sizes, enabling attackers to execute arbitrary code during the boot process. The vulnerabilities compromise the secure boot verification chain, undermining the foundational security of affected systems.

Identified Vulnerabilities

The most severe vulnerability, tracked as CVE-2025-21XX, affects GRUB2’s memory allocation functions when parsing configuration files. Below is a list of documented vulnerabilities:

An attacker with physical access or administrative privileges could exploit these flaws to bypass secure boot mechanisms and execute malicious code that persists across system reboots and reinstallations. One particularly severe vulnerability involves improper boundary checking in GRUB2’s parsing function, as shown in the following code snippet:

grub_err_t grub_parser_execute(char *script) {
  grub_parser_t parser = grub_parser_get_current();
  return parser->parse_line(script, read_hook); // No proper input validation
}

Technical analysis indicates that attackers can craft specially formatted configuration entries to trigger buffer overflow conditions, leading to arbitrary code execution during boot. This technique bypasses traditional security controls by executing malicious code before OS-level security mechanisms activate.

Microsoft’s findings emphasize the critical importance of securing the boot process as a foundational defense layer. System administrators should apply emergency patches released by bootloader maintainers in response to Microsoft’s responsible disclosure. For systems that cannot be immediately updated, implementing physical security measures and restricting administrative access is recommended to mitigate the risk of exploitation.

This discovery underscores the growing role of AI-assisted cybersecurity research in uncovering complex vulnerabilities within critical infrastructure components—vulnerabilities that might otherwise remain undetected until actively exploited in the wild.

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