CVE-2024-49504: grub2 Privilege Escalation Vulnerability

CVE-2024-49504 Overview

A security vulnerability has been identified in GRUB2 (GRand Unified Bootloader version 2) that allows attackers with physical access to the GRUB shell to bypass encryption protections and access files on encrypted disks. This bootloader vulnerability undermines the security guarantees provided by full disk encryption, potentially exposing sensitive data to unauthorized parties who gain physical access to affected systems.

Critical Impact

Attackers with physical access can bypass disk encryption protections through the GRUB shell, completely compromising the confidentiality of encrypted data.

Affected Products

• GRUB2 (GRand Unified Bootloader 2)
• Linux distributions using vulnerable GRUB2 versions
• SUSE Linux Enterprise distributions (see vendor advisory)

Discovery Timeline

• 2024-11-13 - CVE-2024-49504 published to NVD
• 2024-11-13 - Last updated in NVD database

Technical Details for CVE-2024-49504

Vulnerability Analysis

This vulnerability in GRUB2 represents a significant security flaw in how the bootloader handles access controls for encrypted disk volumes. The weakness is classified under CWE-276 (Incorrect Default Permissions), indicating that the bootloader fails to properly enforce access restrictions when operating in shell mode.

When a system is configured with full disk encryption (such as LUKS), users expect that without the proper decryption key or passphrase, the contents of the encrypted volume remain inaccessible. However, this vulnerability allows an attacker who can access the GRUB shell—typically by interrupting the boot process—to read files from encrypted disks without proper authorization.

The physical access requirement limits the exploitability of this vulnerability to scenarios where an attacker has direct access to the target machine, such as stolen laptops, compromised data centers, or insider threat scenarios. Despite this limitation, the ability to completely bypass disk encryption represents a severe breach of data confidentiality.

Root Cause

The root cause of CVE-2024-49504 is an incorrect default permissions issue (CWE-276) in GRUB2's handling of encrypted disk access. The bootloader fails to properly enforce access control restrictions when operating in interactive shell mode, allowing unauthorized file system access to encrypted volumes. This permission model flaw means that security boundaries expected by disk encryption are not maintained at the bootloader level.

Attack Vector

The attack requires physical access to the target system. An attacker must be able to interact with the boot process to access the GRUB shell. Once in the GRUB shell, the attacker can leverage this vulnerability to access files on encrypted disks that should otherwise be protected.

The attack scenario typically involves:

1. The attacker gains physical access to a target machine with encrypted disks
2. The attacker interrupts the normal boot process to access the GRUB shell
3. Through the GRUB shell, the attacker exploits improper permission handling to access encrypted disk contents
4. Sensitive data from the encrypted volume is exfiltrated

This attack bypasses the fundamental security guarantee of full disk encryption—that data remains confidential without the decryption credentials.

Detection Methods for CVE-2024-49504

Indicators of Compromise

• Unexpected boot interruptions or evidence of GRUB shell access in system logs
• Physical tampering indicators on server or workstation hardware
• Unauthorized access to sensitive files that should have been protected by encryption
• Evidence of boot configuration modifications

Detection Strategies

• Implement physical security monitoring and tamper detection for critical systems
• Enable and monitor boot logging to detect unauthorized GRUB shell access attempts
• Deploy endpoint detection solutions that can identify boot-time anomalies
• Implement hardware security modules (HSM) or TPM-based boot attestation

Monitoring Recommendations

• Establish baseline boot behavior and alert on deviations
• Monitor for unauthorized physical access to data center equipment
• Implement chain-of-custody logging for portable devices with encrypted disks
• Use SentinelOne's endpoint protection to detect post-exploitation activities

How to Mitigate CVE-2024-49504

Immediate Actions Required

• Apply vendor security patches for GRUB2 when available from your distribution
• Enable GRUB password protection to restrict shell access
• Implement Secure Boot to validate bootloader integrity
• Restrict physical access to systems containing sensitive encrypted data

Patch Information

Organizations should monitor the SUSE Bug Report CVE-2024-49504 for patch availability and apply updates as they become available from their Linux distribution vendor. GRUB2 updates typically require bootloader reinstallation and may require Secure Boot key re-enrollment.

Workarounds

• Configure GRUB password protection to prevent unauthorized shell access by setting GRUB_PASSWORD in GRUB configuration
• Enable UEFI Secure Boot to ensure only signed bootloaders can execute
• Implement TPM-based measured boot to detect bootloader tampering
• Apply physical security controls including locked server rooms and tamper-evident seals on critical systems
• Consider using additional pre-boot authentication mechanisms

# Configuration example - Enable GRUB password protection
# Generate a hashed password
grub-mkpasswd-pbkdf2

# Add to /etc/grub.d/40_custom:
# set superusers="admin"
# password_pbkdf2 admin <generated-hash>

# Regenerate GRUB configuration
grub-mkconfig -o /boot/grub/grub.cfg