CVE-2022-2601

What it actually does

Buffer overflow in grub_font_construct_glyph() when processing a malicious PF2 font causes max_glyph_size miscalculation, undersized heap allocation, and subsequent out-of-bounds write that can circumvent Secure Boot.

Why it matters to the business

Attackers could load unauthorized code during the boot process on systems using GRUB2, bypassing firmware protections and potentially compromising the entire system before the OS loads; widespread impact on Fedora and multiple Red Hat Enterprise Linux variants increases urgency for organizations relying on Secure Boot.

How an attack unfolds

An attacker supplies a crafted PF2 font file that is processed by GRUB during boot; the font triggers an integer miscalculation leading to a too-small buffer allocation followed by an out-of-bounds write that overwrites heap structures, ultimately allowing execution of attacker-controlled code that evades Secure Boot verification.

How to fix it

Upgrade GRUB2 to a version containing the fix for the glyph-size calculation in grub_font_construct_glyph(); rebuild and reinstall bootloader images on all affected Fedora and Red Hat Enterprise Linux systems; re-enable or verify Secure Boot after patching.

How to confirm the fix worked

Confirm updated GRUB2 package versions are installed on all affected systems; attempt to load a test PF2 font that previously triggered the overflow and verify no crash or out-of-bounds write occurs; re-validate Secure Boot measurements after update.

Typical attack path

1. Prepare a malicious PF2 font file designed to overflow grub_font_construct_glyph()
2. Place the font in a location read by GRUB at boot time (e.g., via bootloader configuration or filesystem)
3. Trigger boot on the target system so GRUB parses the font
4. Exploit the resulting heap out-of-bounds write to modify control flow or load unsigned code
5. Bypass Secure Boot and execute arbitrary early-boot code

How to detect it

Review bootloader logs and early-boot audit records for unexpected font loading or GRUB crashes; examine filesystem artifacts for recently added PF2 files in bootloader directories; correlate with any post-boot anomalies indicating unsigned code execution.

What your security team should do

• Prioritize patching GRUB2 on all Fedora and Red Hat Enterprise Linux systems within the next maintenance window
• Inventory bootloaders and confirm Secure Boot is active before and after remediation
• Monitor upstream GRUB2 releases for the exact fixed version and schedule immediate deployment once available
• Test patched images in a non-production environment to ensure boot integrity is preserved