CVE-2024-56573

What it actually does

The EFI stub incorrectly passes cmdline_ptr (an out-parameter pointing to caller stack) instead of the pool-allocated cmdline to free_pool() on error paths, resulting in an invalid free that can corrupt memory or cause undefined behavior.

Why it matters to the business

Low-probability boot-time instability or crashes on EFI Linux systems; minimal operational disruption given low exploit maturity and single downstream dependent.

How an attack unfolds

An attacker triggers the failure path in the EFI stub (e.g., via malformed command-line handling during boot) to force the wrong pointer into free_pool(), leading to memory corruption that may be leveraged for further kernel compromise.

How to fix it

Apply the upstream fix in commit d173aee5709bd0994d216d60589ec67f8b11376a or upgrade affected packages to the listed fixed versions (e.g., keystone 2:9.3.0-0ubuntu3 on Ubuntu 16.04 LTS). Rebuild and reboot into the patched kernel.

How to confirm the fix worked

Verify kernel source contains the corrected free_pool(cmdline) call; confirm running kernel version includes the patch via uname or package manager; test EFI boot under error conditions.

Typical attack path

1. Gain ability to influence EFI stub boot parameters or induce allocation failure
2. Trigger error path that invokes free_pool with cmdline_ptr
3. Cause invalid memory free leading to corruption or crash
4. Escalate via resulting kernel memory state if exploitation succeeds

How to detect it

Review kernel logs for oops, panic, or memory corruption messages during EFI boot; inspect for unexpected free operations in the stub; correlate with boot parameter changes.

What your security team should do

• Prioritize kernel updates on all EFI-based systems within standard change windows
• Monitor EPSS and KEV status for any future increase in exploit activity
• Include the fixed commit in automated kernel build pipelines