Microsoft Uncovers Several Vulnerabilities in GRUB2, U-Boot, Barebox Bootloaders Using Copilot

Microsoft has discovered multiple critical vulnerabilities affecting widely used bootloaders including GRUB2, U-Boot, and Barebox.

These security flaws potentially expose systems to sophisticated boot-level attacks that could compromise devices before operating systems even initialize, allowing attackers to gain persistent and nearly undetectable control over affected systems.

The vulnerabilities impact thousands of Linux systems and embedded devices that rely on these open-source bootloaders to initialize hardware and load operating systems.

GRUB2 (Grand Unified Bootloader version 2) is particularly concerning given its widespread adoption across enterprise Linux distributions and some secure boot implementations.

U-Boot and Barebox vulnerabilities affect numerous embedded systems, IoT devices, and network appliances, creating a vast attack surface across industries.

Microsoft researchers noted these flaws during a proactive security review using their AI-powered Copilot tool to analyze bootloader codebases.

The company’s security team discovered that specific memory handling functions within these bootloaders fail to properly validate input sizes, potentially allowing attackers to execute arbitrary code during the boot process.

These vulnerabilities exist in the secure boot verification chain, potentially undermining the foundational security these systems are built upon.

Vulnerabilities

The most severe vulnerability, tracked as CVE-2025-21XX, affects GRUB2’s memory allocation functions when parsing configuration files.

Here below we have mentioned all the vulnerabilities:-

An attacker with physical access or administrative privileges could exploit this flaw to bypass secure boot mechanisms and execute malicious code that persists across system reboots and reinstallations.

One particularly concerning vulnerability involves improper boundary checking in GRUB2’s parsing function, as demonstrated in this vulnerable code segment:-

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
}

The technical analysis reveals that attackers could craft specially formatted configuration entries that trigger buffer overflow conditions, allowing arbitrary code execution during boot.

This exploitation technique bypasses traditional security controls by gaining execution before the operating system security features activate.

Microsoft’s discovery underscores the critical importance of securing the boot process as a fundamental layer of defense.

System administrators are advised to apply emergency patches that bootloader maintainers have released in response to Microsoft’s responsible disclosure.

For systems that cannot be immediately updated, Microsoft recommends implementing physical security measures and restricting administrative access to mitigate the risk of exploitation.

This discovery highlights the growing role of AI-assisted cybersecurity research in identifying complex vulnerabilities in critical infrastructure components that might otherwise remain undiscovered until exploited in the wild.

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