AI-Powered Bug Hunt: How Microsoft Used Copilot to Discover Critical Vulnerabilities in GRUB2

Microsoft Uses AI to Uncover 11 GRUB2 Bootloader Vulnerabilities

Last week, Microsoft revealed the discovery of 11 security vulnerabilities in GRUB2, an open-source Linux bootloader. The findings highlight a significant security risk: if exploited, these flaws could compromise the operating system and give attackers full access to user data.

But here’s the twist—Microsoft’s AI assistant, Security Copilot, played a key role in the investigation.

🔧 Why Microsoft Investigated GRUB2

GRUB2 is a critical part of many Linux-based systems. Any vulnerability in it could allow attackers to tamper with how the OS starts up—bypassing security checks and potentially running malicious code before the system is even fully loaded. Due to the high-risk nature of bootloaders, Microsoft took a proactive step in auditing the codebase, focusing on GRUB2.

🤖 Enter AI: Microsoft Security Copilot

To aid in the analysis, Microsoft deployed a custom version of Copilot, their AI-powered assistant, fine-tuned for cybersecurity tasks. While AI alone wasn’t enough to find and confirm every flaw, it dramatically accelerated the discovery process.

The full workflow included:

• AI-assisted code review

• Static analysis

• Fuzzing

• Manual audits

🔍 AI in Action: Code Review with Copilot

In one example, engineers used Copilot to analyze GRUB2 modules responsible for:

• Networking

• Filesystem access

• Cryptographic operations

Copilot flagged five functions related to filesystem mounting as potentially vulnerable. Here’s how it broke down:

• 3 false positives

• 1 non-exploitable

• 1 critical vulnerability confirmed

This small success laid the foundation for broader AI-powered pattern detection.

📁 Chaining AI Insight to Find More Bugs

Once one confirmed bug was validated, engineers asked Copilot to search for similar code patterns across GRUB2. This led to the discovery of multiple vulnerabilities in handlers for different filesystems:

• UFS

• SquashFS (Squash4)

• ReiserFS

• JFS

• RomFS

• UDF

• HFS

Microsoft provided a deep dive into the JFS vulnerability, where an attacker-controlled parameter could trigger a buffer overflow and enable arbitrary code execution.

Although GRUB2 had some internal protections in place, Microsoft found that many of these checks were inconsistently applied, leaving the door open for exploit chains.

🛡️ Beyond GRUB2: U-Boot and Barebox Also Affected

The team didn’t stop at GRUB2. Using the same Copilot-guided methodology, they also uncovered:

• 4 vulnerabilities in U-Boot

• 5 vulnerabilities in Barebox

All GRUB2 issues were fixed as of February 2025, and the most critical flaw—found in the SquashFS handler—received a CVSS score of 7.8 out of 10, indicating high severity.

💡 The Bigger Picture: AI + Security = Faster Response

This investigation showcases how AI, when paired with traditional tools and human expertise, can supercharge the hunt for complex security flaws in massive codebases. While Security Copilot didn’t work magic on its own, it proved to be a valuable tool in narrowing down high-risk areas for human analysts to explore.

As AI continues to mature, tools like this may become standard practice for open-source security audits, enabling faster threat detection and response—especially in systems as foundational as bootloaders.