Linux Grub Read Command Buffer Overflow Vulnerability Enabling Potential Secure Boot Bypass

A newly disclosed vulnerability in the GRUB2 bootloader’s read command (CVE-2025-0690) has raised concerns about potential Secure Boot bypasses and heap memory corruption in Linux systems. 

Red Hat Product Security rates this integer overflow flaw as moderately severe. It could enable attackers with physical access and elevated privileges to execute arbitrary code or undermine Secure Boot protections.

The vulnerability originates in GRUB2’s keyboard input handling via its read command. The command stores the input length in a 32-bit integer variable when processing user input. 

During iterative buffer reallocation, tremendous input values can cause this integer to overflow, triggering an out-of-bounds write in a heap-based buffer. 

This memory corruption could destabilize GRUB’s internal data structures, creating opportunities to subvert Secure Boot’s signature verification process a critical defense against unauthorized operating system or kernel-level malware.

Red Hat’s CVSS v3.1 scoring (6.1) reflects the attack’s constraints: it requires physical access, high privileges, and user interaction. 

However, successful exploitation could grant full control over the boot process, compromising confidentiality, integrity, and availability. 

The weakness chains CWE-190 (Integer Overflow) to CWE-787 (Out-of-Bounds Write), enabling scenarios ranging from denial-of-service crashes to arbitrary code execution.

Affected Systems and Patch Status

The vulnerability impacts:

• Red Hat Enterprise Linux (RHEL) 9 (grub2 package)
• Red Hat OpenShift Container Platform 4 (rhcos component)

Legacy systems like RHEL 7 and 8 remain theoretically vulnerable but are no longer within Red Hat’s support scope. 

Notably, all prior package versions in affected product streams should be considered at risk until explicitly ruled out.

As of February 2025, no mitigations meeting Red Hat’s deployment criteria of stability, scalability, and ease of use are available. While awaiting patches, system administrators must weigh physical access controls against operational requirements.

Secure Boot relies on cryptographic verification of boot components to prevent unauthorized code execution. By exploiting this flaw, attackers could:

• Overwrite GRUB’s memory structures to load unsigned bootloaders or kernels
• Bypass signature checks by corrupting validation routines
• Establish persistent footholds prior to operating system initialization

While the attack complexity is high, the stakes are elevated in shared or high-security environments where physical access barriers might be circumvented. 

Red Hat emphasizes that exploitation would likely involve multi-stage attacks combining social engineering and privilege escalation.

Cybersecurity researchers highlight parallels with BootHole (2020), another GRUB2 flaw that compromised Secure Boot. However, CVE-2025-0690’s reliance on physical access reduces its remote attack potential.

Mitigations

This vulnerability underscores persistent challenges in bootloader security:

• Heap management complexities in low-level system software
• Legacy code risks as GRUB2 evolves to support UEFI and modern hardware
• Trust chain vulnerabilities beneath operating system protections

According to the advisory, The Linux community faces renewed pressure to accelerate the development of memory-safe bootloaders like Rust-based alternatives, though migration timelines remain uncertain.

As firmware-level attacks gain sophistication, this flaw serves as a reminder that secure boot processes demand continuous scrutiny—even in mature open-source projects.

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