CVE-2022-28736

What it actually does

Use-after-free in grub_cmd_chainloader() triggered by repeated chainloader invocations allows memory reuse that can expose sensitive data or enable arbitrary code execution when an attacker influences GRUB2 memory layout.

Why it matters to the business

Compromise of the bootloader can give an attacker persistent control over system startup, enabling full machine takeover, data theft, or installation of boot-level malware across all affected GNU GRUB2 deployments; low EPSS and no KEV listing reduce immediate external risk but local impact remains severe.

How an attack unfolds

An attacker with local access invokes the chainloader command multiple times while manipulating GRUB2 memory allocations to trigger the use-after-free, then leverages the resulting dangling pointer for information disclosure or to execute arbitrary code during the boot process.

How to fix it

Upgrade GNU GRUB2 to a version that resolves the use-after-free in grub_cmd_chainloader(); until a fixed release is available, restrict use of the chainloader command and limit local access to boot configuration files.

How to confirm the fix worked

Confirm GRUB2 version is updated past the vulnerable release, review boot scripts for repeated chainloader usage, and test that multiple chainloader invocations no longer produce memory corruption indicators in debug builds.

Typical attack path

1. Obtain local or physical access to a system using GNU GRUB2
2. Modify or script boot configuration to execute chainloader repeatedly
3. Control memory allocation patterns to trigger the use-after-free
4. Reuse freed memory for code execution or data exfiltration at boot time

How to detect it

Examine GRUB2 debug logs or console output for repeated chainloader command execution; inspect memory dumps or core files from boot failures for signs of freed-memory reuse; correlate with any local user activity that alters boot entries.

What your security team should do

• Prioritize patching GNU GRUB2 on all affected systems once fixed packages are released
• Audit bootloader configurations to remove or restrict chainloader usage where possible
• Enforce least-privilege access to boot media and configuration files
• Monitor for new GRUB2 releases and update EPSS/KEV status tracking