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Microsoft Security Copilot, an AI-powered cybersecurity assistant, has autonomously uncovered 20 critical vulnerabilities in popular Linux bootloaders, including GRUB2, U-Boot, and Barebox. These flaws allow attackers to bypass Secure Boot, install undetectable bootkits, and persist even after OS reinstallation or hard disk replacement.
Key Vulnerabilities Identified
The AI first analyzed high-risk areas (networking, filesystems, cryptographic signatures) before focusing on filesystem-related flaws. After manual verification, one exploitable vulnerability (an integer overflow) was confirmed, leading to the discovery of similar patterns in other files.
Critical CVEs in GRUB2
- CVE-2025-0678: Integer overflow in Squash4 file handling (CVSS 7.8)
- CVE-2024-56737: Buffer overflow in HFS filesystem mounting
- CVE-2024-56738: Side-channel attack in non-constant-time cryptographic comparisons
- CVE-2025-1118: `dump` command allows arbitrary memory reads
Bootloaders are particularly vulnerable due to lacking modern OS protections (no DEP, ASLR, stack guards). GRUB2, written in C, is especially risky due to its large attack surface (filesystem parsers, network support).
Source: Microsoft Security Blog
You Should Know: How to Detect & Mitigate Bootloader Exploits
1. Verify Secure Boot Status (Linux)
mokutil --sb-state
If disabled, enable Secure Boot via BIOS/UEFI settings.
2. Check GRUB2 Version for Vulnerabilities
grub-install --version
Patch immediately if outdated.
3. Validate Bootloader Integrity
sudo bootctl status
Look for “Secure Boot: enabled” and “Boot Loader: signed”.
4. Disable Risky GRUB2 Commands
Edit `/etc/default/grub` and append:
GRUB_DISABLE_OS_PROBER=true GRUB_DISABLE_RECOVERY=true
Then update GRUB:
sudo update-grub
5. Monitor Boot Process via Auditd (Linux)
sudo auditctl -w /boot/grub/ -p wa -k grub_mod
6. Windows: Check Boot Manager (PowerShell)
Confirm-SecureBootUEFI Get-WindowsBootEntry | Format-List
7. Mitigation for CVE-2025-0678 (Squash4 Exploit)
chmod 600 /boot/grub/.mod
What Undercode Say
Bootloader attacks are stealthy and persistent, often surviving disk wipes. Key takeaways:
– Always enable Secure Boot.
– Patch GRUB2/U-Boot immediately.
– Restrict physical access (evil maid attacks).
– Use hardware TPMs for measured boot.
– Monitor `/boot` for unauthorized changes:
sudo tripwire --check
Expected Output:
Secure Boot: enabled Boot Loader: GRUB2 v2.06 (signed) No unsigned modules detected.
For advanced users:
efivar -l | grep -i boot
Lists UEFI boot variables for forensic analysis.
Expected Output: A hardened boot environment with active monitoring and patched vulnerabilities.
References:
Reported By: Bernardi Manuel – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
