CVE-2024-56738

What it actually does

The grub_crypto_memcmp function in GRUB2 through 2.12 performs a non-constant-time memory comparison, enabling timing-based side-channel attacks that can leak cryptographic material.

Why it matters to the business

Attackers may recover sensitive keys or secrets used during the boot process, undermining system integrity and confidentiality on affected devices and increasing risk of unauthorized access or persistent compromise.

How an attack unfolds

An attacker with local or physical access observes minute timing differences when the vulnerable comparison function processes attacker-controlled data versus secret values, allowing statistical inference of the secret over multiple measurements.

How to fix it

Update GRUB2 to a version implementing constant-time comparison in grub_crypto_memcmp; for the listed Firefox packages on Ubuntu 14.04 LTS apply the fixed version 50.0+build2-0ubuntu0.14.04.2.

How to confirm the fix worked

Confirm GRUB2 version is newer than 2.12 with the constant-time memcmp patch applied and verify no timing variance in comparison benchmarks.

Typical attack path

1. Obtain local or physical access to a system using vulnerable GRUB2
2. Craft inputs or observe boot-time cryptographic operations
3. Measure execution timing of grub_crypto_memcmp
4. Apply statistical analysis to recover secret material

How to detect it

Examine boot logs and timing analysis artifacts on systems with physical access history; look for repeated local access patterns around boot operations.

What your security team should do

• Prioritize patching GRUB2 on all bootable systems within the next maintenance window
• Audit boot loader configurations for exposure of cryptographic material
• Monitor for local access attempts on high-value endpoints